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Question 1
Incorrect
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Which of the following is a DNA stop codon?
Your Answer: CCG
Correct Answer: TAG
Explanation:Mutations are changes in the DNA of a cell. There are different types of mutations, including missense mutations, nonsense mutations, point mutations, frameshift mutations, and silent mutations. Missense mutations alter the codon, resulting in a different amino acid in the protein product. Nonsense mutations change a codon that specifies an amino acid to a stop codon, which prematurely stops the translation process. Point mutations involve a single change in one base of the gene sequence. Frameshift mutations occur when a number of nucleotides are inserted of deleted, causing a shift in the sequence and a different translation than the original. Silent mutations code for the same amino acid. Stop codons are nucleotide triplets that signal the end of the translation process. There are three types of stop codons: TAA, TAG, and TGA. When these codons undergo DNA transcription, they change to UAA, UAG, and UGA, which are the stop codons found in RNA molecules.
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This question is part of the following fields:
- Genetics
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Question 2
Incorrect
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What gene is linked to frontotemporal dementia with parkinsonism?
Your Answer: PSEN-1
Correct Answer: MAPT
Explanation:FTDP-17 is a type of frontotemporal dementia that results from a mutation in the MAPT gene found on chromosome 17. The MAPT gene is responsible for producing Tau protein.
Genes Associated with Dementia
Dementia is a complex disorder that can be caused by various genetic and environmental factors. Several genes have been implicated in different forms of dementia. For instance, familial Alzheimer’s disease, which represents less than 1-6% of all Alzheimer’s cases, is associated with mutations in PSEN1, PSEN2, APP, and ApoE genes. These mutations are inherited in an autosomal dominant pattern. On the other hand, late-onset Alzheimer’s disease is a genetic risk factor associated with the ApoE gene, particularly the APOE4 allele. However, inheriting this allele does not necessarily mean that a person will develop Alzheimer’s.
Other forms of dementia, such as familial frontotemporal dementia, Huntington’s disease, CADASIL, and dementia with Lewy bodies, are also associated with specific genes. For example, C9orf72 is the most common mutation associated with familial frontotemporal dementia, while Huntington’s disease is caused by mutations in the HTT gene. CADASIL is associated with mutations in the Notch3 gene, while dementia with Lewy bodies is associated with the APOE, GBA, and SNCA genes.
In summary, understanding the genetic basis of dementia is crucial for developing effective treatments and preventive measures. However, it is important to note that genetics is only one of the many factors that contribute to the development of dementia. Environmental factors, lifestyle choices, and other health conditions also play a significant role.
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This question is part of the following fields:
- Genetics
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Question 3
Correct
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What is the primary constituent of the neurofibrillary tangles observed in Alzheimer's disease?
Your Answer: Tau
Explanation:Tau and Tauopathies
Tau proteins are essential for maintaining the stability of microtubules in neurons. Microtubules provide structural support to the cell and facilitate the transport of molecules within the cell. Tau proteins are predominantly found in the axons of neurons and are absent in dendrites. The gene that codes for tau protein is located on chromosome 17.
When tau proteins become hyperphosphorylated, they clump together, forming neurofibrillary tangles. This process leads to the disintegration of cells, which is a hallmark of several neurodegenerative disorders collectively known as tauopathies.
The major tauopathies include Alzheimer’s disease, Pick’s disease (frontotemporal dementia), progressive supranuclear palsy, and corticobasal degeneration. These disorders are characterized by the accumulation of tau protein in the brain, leading to the degeneration of neurons and cognitive decline. Understanding the role of tau proteins in these disorders is crucial for developing effective treatments for these devastating diseases.
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This question is part of the following fields:
- Genetics
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Question 4
Correct
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Identify the genetic trait that is inherited through the mitochondria.
Your Answer: Leber's hereditary optic neuropathy
Explanation:Inheritance Patterns and Examples
Autosomal Dominant:
Neurofibromatosis type 1 and 2, tuberous sclerosis, achondroplasia, Huntington disease, and Noonan’s syndrome are all examples of conditions that follow an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene is needed to cause the condition.Autosomal Recessive:
Phenylketonuria, homocystinuria, Hurler’s syndrome, galactosaemia, Tay-Sach’s disease, Friedreich’s ataxia, Wilson’s disease, and cystic fibrosis are all examples of conditions that follow an autosomal recessive inheritance pattern. This means that two copies of the mutated gene are needed to cause the condition.X-Linked Dominant:
Vitamin D resistant rickets and Rett syndrome are examples of conditions that follow an X-linked dominant inheritance pattern. This means that the mutated gene is located on the X chromosome and only one copy of the gene is needed to cause the condition.X-Linked Recessive:
Cerebellar ataxia, Hunter’s syndrome, and Lesch-Nyhan are examples of conditions that follow an X-linked recessive inheritance pattern. This means that the mutated gene is located on the X chromosome and two copies of the gene are needed to cause the condition.Mitochondrial:
Leber’s hereditary optic neuropathy and Kearns-Sayre syndrome are examples of conditions that follow a mitochondrial inheritance pattern. This means that the mutated gene is located in the mitochondria and is passed down from the mother to her offspring. -
This question is part of the following fields:
- Genetics
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Question 5
Correct
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What is a true statement about Angelman syndrome?
Your Answer: It is caused by deleted material from the maternal chromosome
Explanation:Genomic Imprinting and its Role in Psychiatric Disorders
Genomic imprinting is a phenomenon where a piece of DNA behaves differently depending on whether it is inherited from the mother of the father. This is because DNA sequences are marked of imprinted in the ovaries and testes, which affects their expression. In psychiatry, two classic examples of genomic imprinting disorders are Prader-Willi and Angelman syndrome.
Prader-Willi syndrome is caused by a deletion of chromosome 15q when inherited from the father. This disorder is characterized by hypotonia, short stature, polyphagia, obesity, small gonads, and mild mental retardation. On the other hand, Angelman syndrome, also known as Happy Puppet syndrome, is caused by a deletion of 15q when inherited from the mother. This disorder is characterized by an unusually happy demeanor, developmental delay, seizures, sleep disturbance, and jerky hand movements.
Overall, genomic imprinting plays a crucial role in the development of psychiatric disorders. Understanding the mechanisms behind genomic imprinting can help in the diagnosis and treatment of these disorders.
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This question is part of the following fields:
- Genetics
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Question 6
Correct
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Can you provide an accurate statement about the use of pairwise and probandwise concordance rates in twin studies?
Your Answer: Probandwise concordance rates are preferred for genetic counselling
Explanation:Both MZ and DZ twins can be analyzed using pairwise and probandwise rates, but probandwise rates are more beneficial in genetic counseling scenarios as they provide information specific to individuals.
Concordance rates are used in twin studies to investigate the genetic contribution to a trait of condition. Concordance refers to the presence of the same trait of condition in both members of a twin pair. There are two main methods of calculating twin concordance rates: pairwise and probandwise. These methods produce different results and are calculated differently. The probandwise method is generally preferred as it provides more meaningful information in a genetic counseling setting.
The table below shows an example of a population of 100,000 MZ twin pairs, and the pairwise and probandwise concordance rates calculated from this population. Pairwise concordance is the probability that both twins in a pair are affected by the trait of condition. Probandwise concordance is the probability that a twin is affected given that their co-twin is affected. Both methods are conditional probabilities, but pairwise applies to twin pairs, while probandwise applies to individual twins. This is why probandwise is preferred, as it helps predict the risk at the individual level.
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This question is part of the following fields:
- Genetics
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Question 7
Correct
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What is an example of a condition that is inherited in an X-linked dominant pattern?
Your Answer: Rett syndrome
Explanation:Modes of Inheritance
Genetic disorders can be passed down from one generation to the next in various ways. There are four main modes of inheritance: autosomal dominant, autosomal recessive, X-linked (sex-linked), and multifactorial.
Autosomal Dominant Inheritance
Autosomal dominant inheritance occurs when one faulty gene causes a problem despite the presence of a normal one. This type of inheritance shows vertical transmission, meaning it is based on the appearance of the family pedigree. If only one parent is affected, there is a 50% chance of each child expressing the condition. Autosomal dominant conditions often show pleiotropy, where a single gene influences several characteristics.
Autosomal Recessive Inheritance
In autosomal recessive conditions, a person requires two faulty copies of a gene to manifest a disease. A person with one healthy and one faulty gene will generally not manifest a disease and is labelled a carrier. Autosomal recessive conditions demonstrate horizontal transmission.
X-linked (Sex-linked) Inheritance
In X-linked conditions, the problem gene lies on the X chromosome. This means that all males are affected. Like autosomal conditions, they can be dominant of recessive. Affected males are unable to pass the condition on to their sons. In X-linked recessive conditions, the inheritance pattern is characterised by transmission from affected males to male grandchildren via affected carrier daughters.
Multifactorial Inheritance
Multifactorial conditions result from the interaction between genes from both parents and the environment.
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This question is part of the following fields:
- Genetics
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Question 8
Incorrect
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Which statement accurately describes familial Alzheimer's disease?
Your Answer: The amyloid precursor protein gene is located on chromosome 12
Correct Answer: The presenilin-1 gene is located on chromosome 14
Explanation:Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 9
Incorrect
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Which of the following options correctly orders the phases of mitosis?
Your Answer:
Correct Answer: Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis
Explanation:Cytokinesis: The Final Stage of Cell Division
Cytokinesis is the final stage of cell division, where the cell splits into two daughter cells, each with a nucleus. This process is essential for the growth and repair of tissues in multicellular organisms. In mitosis, cytokinesis occurs after telophase, while in meiosis, it occurs after telophase I and telophase II.
During cytokinesis, a contractile ring made of actin and myosin filaments forms around the cell’s equator, constricting it like a belt. This ring gradually tightens, pulling the cell membrane inward and creating a furrow that deepens until it reaches the center of the cell. Eventually, the furrow meets in the middle, dividing the cell into two daughter cells.
In animal cells, cytokinesis is achieved by the formation of a cleavage furrow, while in plant cells, a cell plate forms between the two daughter nuclei, which eventually develops into a new cell wall. The timing and mechanism of cytokinesis are tightly regulated by a complex network of proteins and signaling pathways, ensuring that each daughter cell receives the correct amount of cytoplasm and organelles.
Overall, cytokinesis is a crucial step in the cell cycle, ensuring that genetic material is equally distributed between daughter cells and allowing for the growth and development of multicellular organisms.
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This question is part of the following fields:
- Genetics
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Question 10
Incorrect
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How can the inheritance pattern of fragile X syndrome be described?
Your Answer:
Correct Answer: X-linked dominant
Explanation:Fragile X Syndrome: A Genetic Disorder Causing Learning Disability and Psychiatric Symptoms
Fragile X Syndrome is a genetic disorder that causes mental retardation, an elongated face, large protruding ears, and large testicles in men. Individuals with this syndrome tend to be shy, avoid eye contact, and have difficulties reading facial expressions. They also display stereotypic movements such as hand flapping. Fragile X Syndrome is the most common inherited cause of learning disability.
The speech of affected individuals is often abnormal, with abnormalities of fluency. This disorder is caused by the amplification of a CGG repeat in the 5 untranslated region of the fragile X mental retardation 1 gene (FMR1). These CGG repeats disrupt synthesis of the fragile X protein (FMRP), which is essential for brain function and growth. The gene is located at Xq27. The greater number of repeats, the more severe the condition, as with other trinucleotide repeat disorders.
The fragile X phenotype typically involves a variety of psychiatric symptoms, including features of autism, attention deficit/hyperactivity disorder, anxiety, and aggression. Both males and females can be affected, but males are more severely affected because they have only one X chromosome. The prevalence estimate of Fragile X Syndrome is 1/3600-4000.
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This question is part of the following fields:
- Genetics
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Question 11
Incorrect
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What is an example of a genetic condition that is inherited in an autosomal recessive manner?
Your Answer:
Correct Answer: Wilson's disease
Explanation:Inheritance Patterns and Examples
Autosomal Dominant:
Neurofibromatosis type 1 and 2, tuberous sclerosis, achondroplasia, Huntington disease, and Noonan’s syndrome are all examples of conditions that follow an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene is needed to cause the condition.Autosomal Recessive:
Phenylketonuria, homocystinuria, Hurler’s syndrome, galactosaemia, Tay-Sach’s disease, Friedreich’s ataxia, Wilson’s disease, and cystic fibrosis are all examples of conditions that follow an autosomal recessive inheritance pattern. This means that two copies of the mutated gene are needed to cause the condition.X-Linked Dominant:
Vitamin D resistant rickets and Rett syndrome are examples of conditions that follow an X-linked dominant inheritance pattern. This means that the mutated gene is located on the X chromosome and only one copy of the gene is needed to cause the condition.X-Linked Recessive:
Cerebellar ataxia, Hunter’s syndrome, and Lesch-Nyhan are examples of conditions that follow an X-linked recessive inheritance pattern. This means that the mutated gene is located on the X chromosome and two copies of the gene are needed to cause the condition.Mitochondrial:
Leber’s hereditary optic neuropathy and Kearns-Sayre syndrome are examples of conditions that follow a mitochondrial inheritance pattern. This means that the mutated gene is located in the mitochondria and is passed down from the mother to her offspring. -
This question is part of the following fields:
- Genetics
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Question 12
Incorrect
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How can the pattern of inheritance that exhibits a knight's move be described?
Your Answer:
Correct Answer: X-linked recessive
Explanation:Inheritance Patterns:
Autosomal Dominant Conditions:
– Can be transmitted from one generation to the next (vertical transmission) through all forms of transmission observed (male to male, male to female, female to female).
– Males and females are affected in equal proportions.
– Usually, one parent is an affected heterozygote and the other is an unaffected homozygote.
– If only one parent is affected, there is a 50% chance that a child will inherit the mutated gene.Autosomal Recessive Conditions:
– Males and females are affected in equal proportions.
– Two copies of the gene must be mutated for a person to be affected.
– Both parents are usually unaffected heterozygotes.
– Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder.X-linked Dominant Conditions:
– Males and females are both affected, with males typically being more severely affected than females.
– The sons of a man with an X-linked dominant disorder will all be unaffected.
– A woman with an X-linked dominant disorder has a 50% chance of having an affected fetus.X-linked Recessive Conditions:
– Males are more frequently affected than females.
– Transmitted through carrier females to their sons (knights move pattern).
– Affected males cannot pass the condition onto their sons.
– A woman who is a carrier of an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers.Y-linked Conditions:
– Every son of an affected father will be affected.
– Female offspring of affected fathers are never affected.Mitochondrial Inheritance:
– Mitochondria are inherited only in the maternal ova and not in sperm.
– Males and females are affected, but always being maternally inherited.
– An affected male does not pass on his mitochondria to his children, so all his children will be unaffected. -
This question is part of the following fields:
- Genetics
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Question 13
Incorrect
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What factor is involved in the development of Alzheimer's disease?
Your Answer:
Correct Answer: All of the above
Explanation:Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 14
Incorrect
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Which statement about Fragile X is not true?
Your Answer:
Correct Answer: It only affects males
Explanation:Fragile X Syndrome: A Genetic Disorder Causing Learning Disability and Psychiatric Symptoms
Fragile X Syndrome is a genetic disorder that causes mental retardation, an elongated face, large protruding ears, and large testicles in men. Individuals with this syndrome tend to be shy, avoid eye contact, and have difficulties reading facial expressions. They also display stereotypic movements such as hand flapping. Fragile X Syndrome is the most common inherited cause of learning disability.
The speech of affected individuals is often abnormal, with abnormalities of fluency. This disorder is caused by the amplification of a CGG repeat in the 5 untranslated region of the fragile X mental retardation 1 gene (FMR1). These CGG repeats disrupt synthesis of the fragile X protein (FMRP), which is essential for brain function and growth. The gene is located at Xq27. The greater number of repeats, the more severe the condition, as with other trinucleotide repeat disorders.
The fragile X phenotype typically involves a variety of psychiatric symptoms, including features of autism, attention deficit/hyperactivity disorder, anxiety, and aggression. Both males and females can be affected, but males are more severely affected because they have only one X chromosome. The prevalence estimate of Fragile X Syndrome is 1/3600-4000.
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This question is part of the following fields:
- Genetics
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Question 15
Incorrect
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Can you identify a condition that falls under the category of tauopathy?
Your Answer:
Correct Answer: Pick's disease
Explanation:Tau and Tauopathies
Tau proteins are essential for maintaining the stability of microtubules in neurons. Microtubules provide structural support to the cell and facilitate the transport of molecules within the cell. Tau proteins are predominantly found in the axons of neurons and are absent in dendrites. The gene that codes for tau protein is located on chromosome 17.
When tau proteins become hyperphosphorylated, they clump together, forming neurofibrillary tangles. This process leads to the disintegration of cells, which is a hallmark of several neurodegenerative disorders collectively known as tauopathies.
The major tauopathies include Alzheimer’s disease, Pick’s disease (frontotemporal dementia), progressive supranuclear palsy, and corticobasal degeneration. These disorders are characterized by the accumulation of tau protein in the brain, leading to the degeneration of neurons and cognitive decline. Understanding the role of tau proteins in these disorders is crucial for developing effective treatments for these devastating diseases.
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This question is part of the following fields:
- Genetics
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Question 16
Incorrect
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What is the estimated percentage of Caucasians who have the homozygous isoform of alcohol dehydrogenase ADH1B*1?
Your Answer:
Correct Answer: 85-95%
Explanation:This question is challenging as it requires an estimation of the percentage of Caucasians who possess two copies of the gene responsible for the slow-acting form of alcohol dehydrogenase.
Genetics and Alcoholism
Alcoholism tends to run in families, and several studies confirm that biological children of alcoholics are more likely to develop alcoholism even when adopted by parents without the condition. Monozygotic twins have a greater concordance rate for alcoholism than dizygotic twins. Heritability estimates range from 45 to 65 percent for both men and women. While genetic differences affect risk, there is no “gene for alcoholism,” and both environmental and social factors weigh heavily on the outcome.
The genes with the clearest contribution to the risk for alcoholism and alcohol consumption are alcohol dehydrogenase 1B (ADH1B) and aldehyde dehydrogenase 2 (ALDH2). The first step in ethanol metabolism is oxidation to acetaldehyde, by ADHs. The second step is metabolism of the acetaldehyde to acetate by ALDHs. Individuals carrying even a single copy of the ALDH2*504K display the “Asian flushing reaction” when they consume even small amounts of alcohol. There is one significant genetic polymorphism of the ALDH2 gene, resulting in allelic variants ALDH2*1 and ALDH2*2, which is virtually inactive. ALDH2*2 is present in about 50 percent of the Taiwanese, Han Chinese, and Japanese populations. It is extremely rare outside Asia. Nearly no individuals of European of African descent carry this allele. ALDH2*504K has repeatedly been demonstrated to have a protective effect against alcohol use disorders.
The three different class I gene loci, ADH1A (alpha), ADH1B (beta), and ADH1C (gamma) are situated close to each other in the region 4q2123. The alleles ADH1C*1 and ADH1B*2 code for fast metabolism of alcohol. The ADH1B*1 slow allele is very common among Caucasians, with approximately 95 percent having the homozygous ADH1B*1/1 genotype and 5 percent having the heterozygous ADH1B*1/2 genotype. The ADH1B*2 allele is the most common allele in Asian populations. In African populations, the ADH1B*1 allele is the most common.
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This question is part of the following fields:
- Genetics
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Question 17
Incorrect
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What is the frequency of the A allele in a population of 100 diploid individuals, where 30 individuals are heterozygous for allele A and 5 individuals are homozygous for allele A?
Your Answer:
Correct Answer: 0.2
Explanation:Hardy-Weinberg Principle and Allele Frequency
Allele frequency refers to the proportion of a population that carries a specific variant at a particular gene locus. It can be calculated by dividing the number of individual alleles of a certain type by the total number of alleles in a population. The Hardy-Weinberg Principle states that both allele and genotype frequencies in a population remain constant from generation to generation unless specific disturbing influences are introduced. To remain in equilibrium, five conditions must be met, including no mutations, no gene flow, random mating, a sufficiently large population, and no natural selection. The Hardy-Weinberg Equation is used to predict the frequency of alleles in a population, and it can be used to estimate the carrier frequency of genetic diseases. For example, if the incidence of PKU is one in 10,000 babies, then the carrier frequency in the general population is 1/50. Couples with a previous child with PKU have a 25% chance of having another affected child.
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This question is part of the following fields:
- Genetics
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Question 18
Incorrect
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What is the equation for Hardy-Weinberg?
Your Answer:
Correct Answer: p² + 2pq + q²= 1
Explanation:Hardy-Weinberg Principle and Allele Frequency
Allele frequency refers to the proportion of a population that carries a specific variant at a particular gene locus. It can be calculated by dividing the number of individual alleles of a certain type by the total number of alleles in a population. The Hardy-Weinberg Principle states that both allele and genotype frequencies in a population remain constant from generation to generation unless specific disturbing influences are introduced. To remain in equilibrium, five conditions must be met, including no mutations, no gene flow, random mating, a sufficiently large population, and no natural selection. The Hardy-Weinberg Equation is used to predict the frequency of alleles in a population, and it can be used to estimate the carrier frequency of genetic diseases. For example, if the incidence of PKU is one in 10,000 babies, then the carrier frequency in the general population is 1/50. Couples with a previous child with PKU have a 25% chance of having another affected child.
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This question is part of the following fields:
- Genetics
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Question 19
Incorrect
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Which stage of the cell cycle is involved in the process of cell division?
Your Answer:
Correct Answer: M Phase
Explanation:The M phase is where cell division takes place through mitosis.
Cytokinesis: The Final Stage of Cell Division
Cytokinesis is the final stage of cell division, where the cell splits into two daughter cells, each with a nucleus. This process is essential for the growth and repair of tissues in multicellular organisms. In mitosis, cytokinesis occurs after telophase, while in meiosis, it occurs after telophase I and telophase II.
During cytokinesis, a contractile ring made of actin and myosin filaments forms around the cell’s equator, constricting it like a belt. This ring gradually tightens, pulling the cell membrane inward and creating a furrow that deepens until it reaches the center of the cell. Eventually, the furrow meets in the middle, dividing the cell into two daughter cells.
In animal cells, cytokinesis is achieved by the formation of a cleavage furrow, while in plant cells, a cell plate forms between the two daughter nuclei, which eventually develops into a new cell wall. The timing and mechanism of cytokinesis are tightly regulated by a complex network of proteins and signaling pathways, ensuring that each daughter cell receives the correct amount of cytoplasm and organelles.
Overall, cytokinesis is a crucial step in the cell cycle, ensuring that genetic material is equally distributed between daughter cells and allowing for the growth and development of multicellular organisms.
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This question is part of the following fields:
- Genetics
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Question 20
Incorrect
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How can the inheritance pattern of a knight's move be demonstrated?
Your Answer:
Correct Answer: Duchenne muscular dystrophy
Explanation:The only X-linked condition among the 5 options is Duchenne muscular dystrophy.
Modes of Inheritance
Genetic disorders can be passed down from one generation to the next in various ways. There are four main modes of inheritance: autosomal dominant, autosomal recessive, X-linked (sex-linked), and multifactorial.
Autosomal Dominant Inheritance
Autosomal dominant inheritance occurs when one faulty gene causes a problem despite the presence of a normal one. This type of inheritance shows vertical transmission, meaning it is based on the appearance of the family pedigree. If only one parent is affected, there is a 50% chance of each child expressing the condition. Autosomal dominant conditions often show pleiotropy, where a single gene influences several characteristics.
Autosomal Recessive Inheritance
In autosomal recessive conditions, a person requires two faulty copies of a gene to manifest a disease. A person with one healthy and one faulty gene will generally not manifest a disease and is labelled a carrier. Autosomal recessive conditions demonstrate horizontal transmission.
X-linked (Sex-linked) Inheritance
In X-linked conditions, the problem gene lies on the X chromosome. This means that all males are affected. Like autosomal conditions, they can be dominant of recessive. Affected males are unable to pass the condition on to their sons. In X-linked recessive conditions, the inheritance pattern is characterised by transmission from affected males to male grandchildren via affected carrier daughters.
Multifactorial Inheritance
Multifactorial conditions result from the interaction between genes from both parents and the environment.
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This question is part of the following fields:
- Genetics
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Question 21
Incorrect
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What is the truth about the genetic factors involved in schizophrenia?
Your Answer:
Correct Answer: The candidate gene COMT is located on chromosome 22
Explanation:Schizophrenia is a complex disorder that is associated with multiple candidate genes. No single gene has been identified as the sole cause of schizophrenia, and it is believed that the more genes involved, the greater the risk. Some of the important candidate genes for schizophrenia include DTNBP1, COMT, NRG1, G72, RGS4, DAOA, DISC1, and DRD2. Among these, neuregulin, dysbindin, and DISC1 are the most replicated and plausible genes, with COMT being the strongest candidate gene due to its role in dopamine metabolism. Low activity of the COMT gene has been associated with obsessive-compulsive disorder and schizophrenia. Neuregulin 1 is a growth factor that stimulates neuron development and differentiation, and increased neuregulin signaling in schizophrenia may suppress the NMDA receptor, leading to lowered glutamate levels. Dysbindin is involved in the biogenesis of lysosome-related organelles, and its expression is decreased in schizophrenia. DISC1 encodes a multifunctional protein that influences neuronal development and adult brain function, and it is disrupted in schizophrenia. It is located at the breakpoint of a balanced translocation identified in a large Scottish family with schizophrenia, schizoaffective disorder, and other major mental illnesses.
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This question is part of the following fields:
- Genetics
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Question 22
Incorrect
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What is the condition caused by inheriting a deletion of chromosome 15q from the father?
Your Answer:
Correct Answer: Prader-Willi
Explanation:Genomic Imprinting and its Role in Psychiatric Disorders
Genomic imprinting is a phenomenon where a piece of DNA behaves differently depending on whether it is inherited from the mother of the father. This is because DNA sequences are marked of imprinted in the ovaries and testes, which affects their expression. In psychiatry, two classic examples of genomic imprinting disorders are Prader-Willi and Angelman syndrome.
Prader-Willi syndrome is caused by a deletion of chromosome 15q when inherited from the father. This disorder is characterized by hypotonia, short stature, polyphagia, obesity, small gonads, and mild mental retardation. On the other hand, Angelman syndrome, also known as Happy Puppet syndrome, is caused by a deletion of 15q when inherited from the mother. This disorder is characterized by an unusually happy demeanor, developmental delay, seizures, sleep disturbance, and jerky hand movements.
Overall, genomic imprinting plays a crucial role in the development of psychiatric disorders. Understanding the mechanisms behind genomic imprinting can help in the diagnosis and treatment of these disorders.
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This question is part of the following fields:
- Genetics
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Question 23
Incorrect
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Which gene, present in an extra copy in individuals with Down's syndrome, is associated with an elevated risk of developing Alzheimer's disease?
Your Answer:
Correct Answer: Amyloid precursor protein
Explanation:The increased likelihood of Alzheimer’s disease in individuals with Down’s syndrome is believed to be linked to their inheritance of an additional copy of the amyloid precursor protein (APP) found on chromosome 21.
Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 24
Incorrect
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In what circumstances does Lyonization always take place?
Your Answer:
Correct Answer: Klinefelter's syndrome
Explanation:Klinefelter’s syndrome is a condition that occurs when a male has one of more extra copies of the X chromosome in their cells. This extra genetic material interferes with male sexual development, causing the testes to function abnormally and reducing testosterone levels. This can lead to delayed of incomplete puberty, genital abnormalities, gynecomastia, reduced facial and body hair, and infertility. Additionally, individuals with Klinefelter’s syndrome may experience learning disabilities, delayed speech and language development, and a shy personality. The syndrome is typically caused by one extra X chromosome in each cell, but can also be caused by two of three extra X chromosomes. The severity of symptoms increases with the number of extra sex chromosomes. Some individuals with Klinefelter’s syndrome have the extra X chromosome in only some of their cells, which can result in milder symptoms. Lyonization, which occurs when there are multiple X chromosomes in a cell, is present to some degree in all individuals with Klinefelter’s syndrome.
Lyonization: The Process of X-Inactivation
The X chromosome is crucial for proper development and cell viability, containing over 1,000 essential genes. However, females carry two copies of the X chromosome, which can result in a potentially toxic double dose of X-linked genes. To address this imbalance, females undergo a process called Lyonization, of X-inactivation, where one of their two X chromosomes is transcriptionally silenced. The silenced X chromosome then condenses into a compact structure known as a Barr body, which remains in a silent state.
X-inactivation occurs randomly, with no preference for the paternal or maternal X chromosome. It takes place early in embryogenesis, soon after fertilization when the dividing conceptus is about 16-32 cells big. This process occurs in all somatic cells of women, but not in germ cells involved in forming gametes. X-inactivation affects most, but not all, genes on the X chromosome. If a cell has more than two X chromosomes, the extra Xs are also inactivated.
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This question is part of the following fields:
- Genetics
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Question 25
Incorrect
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Which condition is characterized by microcephaly?
Your Answer:
Correct Answer: Fetal alcohol syndrome
Explanation:Microcephaly is a characteristic of fetal alcohol syndrome, while macrocephaly is associated with all the other options except for Asperger’s, which is not typically linked to any abnormality in head size.
Microcephaly: A Condition of Small Head Size
Microcephaly is a condition characterized by a small head size. It can be a feature of various conditions, including fetal alcohol syndrome, Down’s syndrome, Edward’s syndrome, Patau syndrome, Angelman syndrome, De Lange syndrome, Prader-Willi syndrome, and Cri-du-chat syndrome. Each of these conditions has its own unique set of symptoms and causes, but they all share the common feature of microcephaly. This condition can have a range of effects on a person’s development, including intellectual disability, seizures, and motor problems. Early diagnosis and intervention can help manage the symptoms and improve outcomes for individuals with microcephaly.
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This question is part of the following fields:
- Genetics
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Question 26
Incorrect
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In which mode of inheritance do typically both parents carry a heterozygous unaffected genotype?
Your Answer:
Correct Answer: Autosomal recessive
Explanation:Inheritance Patterns:
Autosomal Dominant Conditions:
– Can be transmitted from one generation to the next (vertical transmission) through all forms of transmission observed (male to male, male to female, female to female).
– Males and females are affected in equal proportions.
– Usually, one parent is an affected heterozygote and the other is an unaffected homozygote.
– If only one parent is affected, there is a 50% chance that a child will inherit the mutated gene.Autosomal Recessive Conditions:
– Males and females are affected in equal proportions.
– Two copies of the gene must be mutated for a person to be affected.
– Both parents are usually unaffected heterozygotes.
– Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder.X-linked Dominant Conditions:
– Males and females are both affected, with males typically being more severely affected than females.
– The sons of a man with an X-linked dominant disorder will all be unaffected.
– A woman with an X-linked dominant disorder has a 50% chance of having an affected fetus.X-linked Recessive Conditions:
– Males are more frequently affected than females.
– Transmitted through carrier females to their sons (knights move pattern).
– Affected males cannot pass the condition onto their sons.
– A woman who is a carrier of an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers.Y-linked Conditions:
– Every son of an affected father will be affected.
– Female offspring of affected fathers are never affected.Mitochondrial Inheritance:
– Mitochondria are inherited only in the maternal ova and not in sperm.
– Males and females are affected, but always being maternally inherited.
– An affected male does not pass on his mitochondria to his children, so all his children will be unaffected. -
This question is part of the following fields:
- Genetics
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Question 27
Incorrect
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Which statement accurately describes aneuploidy?
Your Answer:
Correct Answer: Only a minority of those with XYY syndrome have an intellectual disability
Explanation:Aneuploidy: Abnormal Chromosome Numbers
Aneuploidy refers to the presence of an abnormal number of chromosomes, which can result from errors during meiosis. Typically, human cells have 23 pairs of chromosomes, but aneuploidy can lead to extra of missing chromosomes. Trisomies, which involve the presence of an additional chromosome, are the most common aneuploidies in humans. However, most trisomies are not compatible with life, and only trisomy 21 (Down’s syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) survive to birth. Aneuploidy can result in imbalances in gene expression, which can lead to a range of symptoms and developmental issues.
Compared to autosomal trisomies, humans are more able to tolerate extra sex chromosomes. Klinefelter’s syndrome, which involves the presence of an extra X chromosome, is the most common sex chromosome aneuploidy. Individuals with Klinefelter’s and XYY often remain undiagnosed, but they may experience reduced sexual development and fertility. Monosomies, which involve the loss of a chromosome, are rare in humans. The only viable human monosomy involves the X chromosome and results in Turner’s syndrome. Turner’s females display a wide range of symptoms, including infertility and impaired sexual development.
The frequency and severity of aneuploidies vary widely. Down’s syndrome is the most common viable autosomal trisomy, affecting 1 in 800 births. Klinefelter’s syndrome affects 1-2 in 1000 male births, while XYY syndrome affects 1 in 1000 male births and Triple X syndrome affects 1 in 1000 births. Turner syndrome is less common, affecting 1 in 5000 female births. Edwards syndrome and Patau syndrome are rare, affecting 1 in 6000 and 1 in 10,000 births, respectively. Understanding the genetic basis and consequences of aneuploidy is important for diagnosis, treatment, and genetic counseling.
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This question is part of the following fields:
- Genetics
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Question 28
Incorrect
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What is the most accurate description of how Pick's disease is inherited?
Your Answer:
Correct Answer: Autosomal dominant
Explanation:Genes Associated with Dementia
Dementia is a complex disorder that can be caused by various genetic and environmental factors. Several genes have been implicated in different forms of dementia. For instance, familial Alzheimer’s disease, which represents less than 1-6% of all Alzheimer’s cases, is associated with mutations in PSEN1, PSEN2, APP, and ApoE genes. These mutations are inherited in an autosomal dominant pattern. On the other hand, late-onset Alzheimer’s disease is a genetic risk factor associated with the ApoE gene, particularly the APOE4 allele. However, inheriting this allele does not necessarily mean that a person will develop Alzheimer’s.
Other forms of dementia, such as familial frontotemporal dementia, Huntington’s disease, CADASIL, and dementia with Lewy bodies, are also associated with specific genes. For example, C9orf72 is the most common mutation associated with familial frontotemporal dementia, while Huntington’s disease is caused by mutations in the HTT gene. CADASIL is associated with mutations in the Notch3 gene, while dementia with Lewy bodies is associated with the APOE, GBA, and SNCA genes.
In summary, understanding the genetic basis of dementia is crucial for developing effective treatments and preventive measures. However, it is important to note that genetics is only one of the many factors that contribute to the development of dementia. Environmental factors, lifestyle choices, and other health conditions also play a significant role.
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This question is part of the following fields:
- Genetics
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Question 29
Incorrect
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Which of the following indicates evidence of linkage based on the LOD score?
Your Answer:
Correct Answer: > 3
Explanation:Linkage and LOD Scores in Genetics
In genetics, when genes are located close to each other on a chromosome, they tend to be inherited together and are referred to as linked genes. Conversely, genes that are far apart of located on different chromosomes are inherited independently and are said to follow independent assortment. To determine the relative distance between two genes, scientists can analyze the offspring of an organism that displays two strongly linked traits and calculate the percentage of offspring where the traits do not co-segregate.
To determine if there is evidence for linkage between two genes, scientists use a statistical method called the LOD score (logarithm of the odds). A LOD score of >3 is considered significant evidence for linkage, while a LOD score of <-2 excludes linkage. The LOD score is calculated by comparing the likelihood of the observed data under the assumption of linkage to the likelihood of the data under the assumption of independent assortment. The LOD score provides a measure of the strength of evidence for linkage between two genes and is widely used in genetic research.
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This question is part of the following fields:
- Genetics
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Question 30
Incorrect
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Which of the following does not follow an autosomal recessive inheritance pattern?
Your Answer:
Correct Answer: Noonan's syndrome
Explanation:Inheritance Patterns and Examples
Autosomal Dominant:
Neurofibromatosis type 1 and 2, tuberous sclerosis, achondroplasia, Huntington disease, and Noonan’s syndrome are all examples of conditions that follow an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene is needed to cause the condition.Autosomal Recessive:
Phenylketonuria, homocystinuria, Hurler’s syndrome, galactosaemia, Tay-Sach’s disease, Friedreich’s ataxia, Wilson’s disease, and cystic fibrosis are all examples of conditions that follow an autosomal recessive inheritance pattern. This means that two copies of the mutated gene are needed to cause the condition.X-Linked Dominant:
Vitamin D resistant rickets and Rett syndrome are examples of conditions that follow an X-linked dominant inheritance pattern. This means that the mutated gene is located on the X chromosome and only one copy of the gene is needed to cause the condition.X-Linked Recessive:
Cerebellar ataxia, Hunter’s syndrome, and Lesch-Nyhan are examples of conditions that follow an X-linked recessive inheritance pattern. This means that the mutated gene is located on the X chromosome and two copies of the gene are needed to cause the condition.Mitochondrial:
Leber’s hereditary optic neuropathy and Kearns-Sayre syndrome are examples of conditions that follow a mitochondrial inheritance pattern. This means that the mutated gene is located in the mitochondria and is passed down from the mother to her offspring. -
This question is part of the following fields:
- Genetics
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Question 31
Incorrect
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What is removed during splicing?
Your Answer:
Correct Answer: Intron
Explanation:Splicing of mRNA
After the transcription of DNA into mRNA, the mRNA undergoes a crucial process known as splicing. This process involves the removal of certain portions of the mRNA, called introns, leaving behind the remaining portions known as exons. The exons are then translated into proteins. The resulting spliced form of RNA is referred to as mature mRNA. This process of splicing is essential for the proper functioning of genes and the production of functional proteins.
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This question is part of the following fields:
- Genetics
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Question 32
Incorrect
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What is the probability that the child of parents who carry one copy of an autosomal recessive disease gene will not be affected by the disease and will not carry the gene?
Your Answer:
Correct Answer: 25%
Explanation:When two individuals who are heterozygous for an autosomal recessive condition have a child, there is a 25% chance that the child will be affected by the condition, a 50% chance that the child will be a carrier of the condition, and a 25% chance that the child will be neither a carrier nor affected by the condition.
Inheritance Patterns:
Autosomal Dominant Conditions:
– Can be transmitted from one generation to the next (vertical transmission) through all forms of transmission observed (male to male, male to female, female to female).
– Males and females are affected in equal proportions.
– Usually, one parent is an affected heterozygote and the other is an unaffected homozygote.
– If only one parent is affected, there is a 50% chance that a child will inherit the mutated gene.Autosomal Recessive Conditions:
– Males and females are affected in equal proportions.
– Two copies of the gene must be mutated for a person to be affected.
– Both parents are usually unaffected heterozygotes.
– Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder.X-linked Dominant Conditions:
– Males and females are both affected, with males typically being more severely affected than females.
– The sons of a man with an X-linked dominant disorder will all be unaffected.
– A woman with an X-linked dominant disorder has a 50% chance of having an affected fetus.X-linked Recessive Conditions:
– Males are more frequently affected than females.
– Transmitted through carrier females to their sons (knights move pattern).
– Affected males cannot pass the condition onto their sons.
– A woman who is a carrier of an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers.Y-linked Conditions:
– Every son of an affected father will be affected.
– Female offspring of affected fathers are never affected.Mitochondrial Inheritance:
– Mitochondria are inherited only in the maternal ova and not in sperm.
– Males and females are affected, but always being maternally inherited.
– An affected male does not pass on his mitochondria to his children, so all his children will be unaffected. -
This question is part of the following fields:
- Genetics
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Question 33
Incorrect
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What is the most accurate approximation for the concordance of autism in monozygotic twins?
Your Answer:
Correct Answer: 65%
Explanation:Autism and Genetics
Research has shown that there is a strong genetic component to autism. In fact, siblings of individuals with autism are significantly more likely to develop the disorder than someone in the general population. Twin studies have also demonstrated the high heritability of autism, but have also highlighted the genetic complexity of the disorder. Monozygotic twins have a concordance rate of 60-90%, while dizygotic twins have a concordance rate closer to 30%. Despite this, the molecular genetics of autism is still not well understood. Copy number variations (CNVs) have been implicated, along with a number of candidate genes. Further research is needed to fully understand the genetic basis of autism.
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This question is part of the following fields:
- Genetics
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Question 34
Incorrect
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Which enzyme is responsible for adding amino acids to RNA molecules to create transfer RNA?
Your Answer:
Correct Answer: Aminoacyl tRNA synthetase
Explanation:The Aminoacyl tRNA Synthetases (AARSs) are a group of enzymes that attach a specific amino acid to its corresponding tRNA molecule. There are 21 different AARS enzymes, each responsible for a different amino acid, except for lysine, which has two AARSs.
Genomics: Understanding DNA, RNA, Transcription, and Translation
Deoxyribonucleic acid (DNA) is a molecule composed of two chains that coil around each other to form a double helix. DNA is organised into chromosomes, and each chromosome is made up of DNA coiled around proteins called histones. RNA, on the other hand, is made from a long chain of nucleotide units and is usually single-stranded. RNA is transcribed from DNA by enzymes called RNA polymerases and is central to protein synthesis.
Transcription is the synthesis of RNA from a DNA template, and it consists of three main steps: initiation, elongation, and termination. RNA polymerase binds at a sequence of DNA called the promoter, and the transcriptome is the collection of RNA molecules that results from transcription. Translation, on the other hand, refers to the synthesis of polypeptides (proteins) from mRNA. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.
The process of translation involves messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transfer RNAs, of tRNAs, connect mRNA codons to the amino acids they encode, while ribosomes are the structures where polypeptides (proteins) are built. Like transcription, translation also consists of three stages: initiation, elongation, and termination. In initiation, the ribosome assembles around the mRNA to be read and the first tRNA carrying the amino acid methionine. In elongation, the amino acid chain gets longer, and in termination, the finished polypeptide chain is released.
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This question is part of the following fields:
- Genetics
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Question 35
Incorrect
-
What is the number of centromeres present in a cell containing 20 chromatids?
Your Answer:
Correct Answer: 10
Explanation:Cytokinesis: The Final Stage of Cell Division
Cytokinesis is the final stage of cell division, where the cell splits into two daughter cells, each with a nucleus. This process is essential for the growth and repair of tissues in multicellular organisms. In mitosis, cytokinesis occurs after telophase, while in meiosis, it occurs after telophase I and telophase II.
During cytokinesis, a contractile ring made of actin and myosin filaments forms around the cell’s equator, constricting it like a belt. This ring gradually tightens, pulling the cell membrane inward and creating a furrow that deepens until it reaches the center of the cell. Eventually, the furrow meets in the middle, dividing the cell into two daughter cells.
In animal cells, cytokinesis is achieved by the formation of a cleavage furrow, while in plant cells, a cell plate forms between the two daughter nuclei, which eventually develops into a new cell wall. The timing and mechanism of cytokinesis are tightly regulated by a complex network of proteins and signaling pathways, ensuring that each daughter cell receives the correct amount of cytoplasm and organelles.
Overall, cytokinesis is a crucial step in the cell cycle, ensuring that genetic material is equally distributed between daughter cells and allowing for the growth and development of multicellular organisms.
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This question is part of the following fields:
- Genetics
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Question 36
Incorrect
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Which allele is believed to have a protective effect against Alzheimer's disease?
Your Answer:
Correct Answer: APOE2
Explanation:APOE3 is considered to have a neutral effect on the risk of developing certain health conditions.
Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 37
Incorrect
-
What is the most accurate estimation of the heritability of schizophrenia?
Your Answer:
Correct Answer: 55%
Explanation:Heritability: Understanding the Concept
Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.
The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:
Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.
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This question is part of the following fields:
- Genetics
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Question 38
Incorrect
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Out of the given conditions, which one is an example of aneuploidy?
Your Answer:
Correct Answer: Down's syndrome
Explanation:Aneuploidy: Abnormal Chromosome Numbers
Aneuploidy refers to the presence of an abnormal number of chromosomes, which can result from errors during meiosis. Typically, human cells have 23 pairs of chromosomes, but aneuploidy can lead to extra of missing chromosomes. Trisomies, which involve the presence of an additional chromosome, are the most common aneuploidies in humans. However, most trisomies are not compatible with life, and only trisomy 21 (Down’s syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) survive to birth. Aneuploidy can result in imbalances in gene expression, which can lead to a range of symptoms and developmental issues.
Compared to autosomal trisomies, humans are more able to tolerate extra sex chromosomes. Klinefelter’s syndrome, which involves the presence of an extra X chromosome, is the most common sex chromosome aneuploidy. Individuals with Klinefelter’s and XYY often remain undiagnosed, but they may experience reduced sexual development and fertility. Monosomies, which involve the loss of a chromosome, are rare in humans. The only viable human monosomy involves the X chromosome and results in Turner’s syndrome. Turner’s females display a wide range of symptoms, including infertility and impaired sexual development.
The frequency and severity of aneuploidies vary widely. Down’s syndrome is the most common viable autosomal trisomy, affecting 1 in 800 births. Klinefelter’s syndrome affects 1-2 in 1000 male births, while XYY syndrome affects 1 in 1000 male births and Triple X syndrome affects 1 in 1000 births. Turner syndrome is less common, affecting 1 in 5000 female births. Edwards syndrome and Patau syndrome are rare, affecting 1 in 6000 and 1 in 10,000 births, respectively. Understanding the genetic basis and consequences of aneuploidy is important for diagnosis, treatment, and genetic counseling.
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This question is part of the following fields:
- Genetics
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Question 39
Incorrect
-
Which condition is inherited in an autosomal dominant pattern?
Your Answer:
Correct Answer: Huntington's disease
Explanation:Inheritance Patterns and Examples
Autosomal Dominant:
Neurofibromatosis type 1 and 2, tuberous sclerosis, achondroplasia, Huntington disease, and Noonan’s syndrome are all examples of conditions that follow an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene is needed to cause the condition.Autosomal Recessive:
Phenylketonuria, homocystinuria, Hurler’s syndrome, galactosaemia, Tay-Sach’s disease, Friedreich’s ataxia, Wilson’s disease, and cystic fibrosis are all examples of conditions that follow an autosomal recessive inheritance pattern. This means that two copies of the mutated gene are needed to cause the condition.X-Linked Dominant:
Vitamin D resistant rickets and Rett syndrome are examples of conditions that follow an X-linked dominant inheritance pattern. This means that the mutated gene is located on the X chromosome and only one copy of the gene is needed to cause the condition.X-Linked Recessive:
Cerebellar ataxia, Hunter’s syndrome, and Lesch-Nyhan are examples of conditions that follow an X-linked recessive inheritance pattern. This means that the mutated gene is located on the X chromosome and two copies of the gene are needed to cause the condition.Mitochondrial:
Leber’s hereditary optic neuropathy and Kearns-Sayre syndrome are examples of conditions that follow a mitochondrial inheritance pattern. This means that the mutated gene is located in the mitochondria and is passed down from the mother to her offspring. -
This question is part of the following fields:
- Genetics
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Question 40
Incorrect
-
Which condition is most commonly linked to copy number variations?
Your Answer:
Correct Answer: Autism
Explanation:Copy Number Variations
Portions of DNA can vary in number, resulting in copy number variations (CNVs). These variations can lead to additional of fewer copies of certain genes, which can affect gene expression and have significant impacts on performance and health. While most CNVs are not clinically significant, they have been linked to conditions such as autism, schizophrenia, and learning disabilities.
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This question is part of the following fields:
- Genetics
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Question 41
Incorrect
-
The most probable diagnosis for a patient with an isolated finding of atrophy of the head of caudate nucleus on a CT scan is:
Your Answer:
Correct Answer: Huntington's disease
Explanation:Huntington’s Disease: Genetics and Pathology
Huntington’s disease is a genetic disorder that follows an autosomal dominant pattern of inheritance. It is caused by a mutation in the Huntington gene, which is located on chromosome 4. The mutation involves an abnormal expansion of a trinucleotide repeat sequence (CAG), which leads to the production of a toxic protein that damages brain cells.
The severity of the disease and the age of onset are related to the number of CAG repeats. Normally, the CAG sequence is repeated less than 27 times, but in Huntington’s disease, it is repeated many more times. The disease shows anticipation, meaning that it tends to worsen with each successive generation.
The symptoms of Huntington’s disease typically begin in the third of fourth decade of life, but in rare cases, they can appear in childhood of adolescence. The most common symptoms include involuntary movements (chorea), cognitive decline, and psychiatric disturbances.
The pathological hallmark of Huntington’s disease is the gross bilateral atrophy of the head of the caudate and putamen, which are regions of the brain involved in movement control. The EEG of patients with Huntington’s disease shows a flattened trace, indicating a loss of brain activity.
Macroscopic pathological findings include frontal atrophy, marked atrophy of the caudate and putamen, and enlarged ventricles. Microscopic findings include neuronal loss and gliosis in the cortex, neuronal loss in the striatum, and the presence of inclusion bodies in the neurons of the cortex and striatum.
In conclusion, Huntington’s disease is a devastating genetic disorder that affects the brain and causes a range of motor, cognitive, and psychiatric symptoms. The disease is caused by a mutation in the Huntington gene, which leads to the production of a toxic protein that damages brain cells. The pathological changes in the brain include atrophy of the caudate and putamen, neuronal loss, and the presence of inclusion bodies.
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This question is part of the following fields:
- Genetics
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Question 42
Incorrect
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How can a group of genetic defects causing a single condition be described?
Your Answer:
Correct Answer: Heterogeneity
Explanation:Pleiotropy refers to a genetic phenomenon where a single gene has an impact on multiple observable traits. This occurs because the gene produces a product that is utilized by various cells. An instance of pleiotropy is the human condition known as PKU (phenylketonuria).
Understanding Heterogeneity in Genetic Diseases
Heterogeneity is a term used to describe the presence of different genetic defects that can cause the same disease. This phenomenon is commonly observed in genetic disorders, where multiple mutations can lead to the same clinical presentation. For instance, the ABO blood group system is an example of heterogeneity, where different combinations of alleles can result in the same blood type.
Understanding heterogeneity is crucial for accurate diagnosis and treatment of genetic diseases. Identifying the specific genetic defect responsible for a particular disease can help tailor therapies and predict disease progression. However, the presence of heterogeneity can also complicate diagnosis and treatment, as different mutations may require different approaches.
Overall, heterogeneity highlights the complexity of genetic diseases and underscores the need for personalized medicine approaches that take into account individual genetic variations.
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This question is part of the following fields:
- Genetics
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Question 43
Incorrect
-
If a woman with cystic fibrosis marries a man who is not a carrier of the CF gene and they conceive a child, what is the likelihood that the child will not be affected by the condition?
Your Answer:
Correct Answer: 1:01
Explanation:Cystic fibrosis (CF) is an autosomal recessive disorder, which means that both parents must carry a copy of the CF gene for their child to be affected. In this scenario, the mother has two copies of the CF gene, while the father has none. As a result, their child will inherit one CF gene and one unaffected gene, making her a carrier but not affected by the disorder. However, it’s important to note that there are over 2000 known mutations of the CF gene, and if a person tests negative for all of them, there is still a 1 in 500 chance that they have an undetectable mutation. Therefore, the probability of the child being unaffected is slightly less than 1 in 1.
Mendelian Inheritance (Pedigrees)
Mendelian inheritance refers to the transmission patterns of genetic conditions caused by a mutation in a single gene. There are four types of Mendelian inheritance patterns: autosomal dominant, autosomal recessive, X-linked recessive, and X-linked dominant. Each pattern follows a predictable inheritance pattern within families.
Autosomal dominant conditions are expressed in individuals who have just one copy of the mutant allele. Affected males and females have an equal probability of passing on the trait to offspring. In contrast, autosomal recessive conditions are clinically manifest only when an individual has two copies of the mutant allele. X-linked recessive traits are fully evident in males because they only have one copy of the X chromosome, while women are rarely affected by X-linked recessive diseases. X-linked dominant disorders are clinically manifest when only one copy of the mutant allele is present.
Common examples of conditions with specific inheritance patterns include neurofibromatosis type 1 and 2, tuberous sclerosis, achondroplasia, Huntington disease, Noonan’s syndrome for autosomal dominant; phenylketonuria, homocystinuria, Hurler’s syndrome, galactosaemia, Tay-Sach’s disease, Friedreich’s ataxia, Wilson’s disease, cystic fibrosis for autosomal recessive; vitamin D resistant rickets, Rett syndrome for X-linked dominant; and cerebellar ataxia, Hunter’s syndrome, Lesch-Nyhan for X-linked recessive.
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This question is part of the following fields:
- Genetics
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Question 44
Incorrect
-
What is the term used to describe genes that are located close to each other on a chromosome and are unlikely to be separated by crossing over?
Your Answer:
Correct Answer: Linked
Explanation:Linkage and LOD Scores in Genetics
In genetics, when genes are located close to each other on a chromosome, they tend to be inherited together and are referred to as linked genes. Conversely, genes that are far apart of located on different chromosomes are inherited independently and are said to follow independent assortment. To determine the relative distance between two genes, scientists can analyze the offspring of an organism that displays two strongly linked traits and calculate the percentage of offspring where the traits do not co-segregate.
To determine if there is evidence for linkage between two genes, scientists use a statistical method called the LOD score (logarithm of the odds). A LOD score of >3 is considered significant evidence for linkage, while a LOD score of <-2 excludes linkage. The LOD score is calculated by comparing the likelihood of the observed data under the assumption of linkage to the likelihood of the data under the assumption of independent assortment. The LOD score provides a measure of the strength of evidence for linkage between two genes and is widely used in genetic research.
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This question is part of the following fields:
- Genetics
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Question 45
Incorrect
-
Which statement accurately describes late onset Alzheimer's disease?
Your Answer:
Correct Answer: The APOE3 variant is considered the neutral variant
Explanation:Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 46
Incorrect
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What is the accurate statement about the pathology of Huntington's disease?
Your Answer:
Correct Answer: There is marked atrophy of the caudate and putamen
Explanation:Huntington’s Disease: Genetics and Pathology
Huntington’s disease is a genetic disorder that follows an autosomal dominant pattern of inheritance. It is caused by a mutation in the Huntington gene, which is located on chromosome 4. The mutation involves an abnormal expansion of a trinucleotide repeat sequence (CAG), which leads to the production of a toxic protein that damages brain cells.
The severity of the disease and the age of onset are related to the number of CAG repeats. Normally, the CAG sequence is repeated less than 27 times, but in Huntington’s disease, it is repeated many more times. The disease shows anticipation, meaning that it tends to worsen with each successive generation.
The symptoms of Huntington’s disease typically begin in the third of fourth decade of life, but in rare cases, they can appear in childhood of adolescence. The most common symptoms include involuntary movements (chorea), cognitive decline, and psychiatric disturbances.
The pathological hallmark of Huntington’s disease is the gross bilateral atrophy of the head of the caudate and putamen, which are regions of the brain involved in movement control. The EEG of patients with Huntington’s disease shows a flattened trace, indicating a loss of brain activity.
Macroscopic pathological findings include frontal atrophy, marked atrophy of the caudate and putamen, and enlarged ventricles. Microscopic findings include neuronal loss and gliosis in the cortex, neuronal loss in the striatum, and the presence of inclusion bodies in the neurons of the cortex and striatum.
In conclusion, Huntington’s disease is a devastating genetic disorder that affects the brain and causes a range of motor, cognitive, and psychiatric symptoms. The disease is caused by a mutation in the Huntington gene, which leads to the production of a toxic protein that damages brain cells. The pathological changes in the brain include atrophy of the caudate and putamen, neuronal loss, and the presence of inclusion bodies.
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This question is part of the following fields:
- Genetics
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Question 47
Incorrect
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A young adult presents with a 2 year history of an unusual movement disorder associated with memory problems. He denies any past psychiatric history but does recall that one of his parents died early from a similar movement problem. Which is the most likely diagnosis?
Your Answer:
Correct Answer: Huntington's disease
Explanation:Huntington’s Disease: Genetics and Pathology
Huntington’s disease is a genetic disorder that follows an autosomal dominant pattern of inheritance. It is caused by a mutation in the Huntington gene, which is located on chromosome 4. The mutation involves an abnormal expansion of a trinucleotide repeat sequence (CAG), which leads to the production of a toxic protein that damages brain cells.
The severity of the disease and the age of onset are related to the number of CAG repeats. Normally, the CAG sequence is repeated less than 27 times, but in Huntington’s disease, it is repeated many more times. The disease shows anticipation, meaning that it tends to worsen with each successive generation.
The symptoms of Huntington’s disease typically begin in the third of fourth decade of life, but in rare cases, they can appear in childhood of adolescence. The most common symptoms include involuntary movements (chorea), cognitive decline, and psychiatric disturbances.
The pathological hallmark of Huntington’s disease is the gross bilateral atrophy of the head of the caudate and putamen, which are regions of the brain involved in movement control. The EEG of patients with Huntington’s disease shows a flattened trace, indicating a loss of brain activity.
Macroscopic pathological findings include frontal atrophy, marked atrophy of the caudate and putamen, and enlarged ventricles. Microscopic findings include neuronal loss and gliosis in the cortex, neuronal loss in the striatum, and the presence of inclusion bodies in the neurons of the cortex and striatum.
In conclusion, Huntington’s disease is a devastating genetic disorder that affects the brain and causes a range of motor, cognitive, and psychiatric symptoms. The disease is caused by a mutation in the Huntington gene, which leads to the production of a toxic protein that damages brain cells. The pathological changes in the brain include atrophy of the caudate and putamen, neuronal loss, and the presence of inclusion bodies.
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This question is part of the following fields:
- Genetics
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Question 48
Incorrect
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What is a true statement regarding the risks of developing schizophrenia based on the Gottesman data?
Your Answer:
Correct Answer: A parent has a 6% chance of developing schizophrenia is their child is affected
Explanation:Schizophrenia Risk According to Gottesman
Irving I. Gottesman conducted family and twin studies in European populations between 1920 and 1987 to determine the risk of developing schizophrenia for relatives of those with the disorder. The following table displays Gottesman’s findings, which show the average lifetime risk for each relationship:
General population: 1%
First cousin: 2%
Uncle/aunt: 2%
Nephew/niece: 4%
Grandchildren: 5%
Parents: 6%
Half sibling: 6%
Full sibling: 9%
Children: 13%
Fraternal twins: 17%
Offspring of dual matings (both parents had schizophrenia): 46%
Identical twins: 48% -
This question is part of the following fields:
- Genetics
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Question 49
Incorrect
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Which statement accurately describes aneuploidy?
Your Answer:
Correct Answer: Babies born with Edward's syndrome often die soon after birth
Explanation:Aneuploidy: Abnormal Chromosome Numbers
Aneuploidy refers to the presence of an abnormal number of chromosomes, which can result from errors during meiosis. Typically, human cells have 23 pairs of chromosomes, but aneuploidy can lead to extra of missing chromosomes. Trisomies, which involve the presence of an additional chromosome, are the most common aneuploidies in humans. However, most trisomies are not compatible with life, and only trisomy 21 (Down’s syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) survive to birth. Aneuploidy can result in imbalances in gene expression, which can lead to a range of symptoms and developmental issues.
Compared to autosomal trisomies, humans are more able to tolerate extra sex chromosomes. Klinefelter’s syndrome, which involves the presence of an extra X chromosome, is the most common sex chromosome aneuploidy. Individuals with Klinefelter’s and XYY often remain undiagnosed, but they may experience reduced sexual development and fertility. Monosomies, which involve the loss of a chromosome, are rare in humans. The only viable human monosomy involves the X chromosome and results in Turner’s syndrome. Turner’s females display a wide range of symptoms, including infertility and impaired sexual development.
The frequency and severity of aneuploidies vary widely. Down’s syndrome is the most common viable autosomal trisomy, affecting 1 in 800 births. Klinefelter’s syndrome affects 1-2 in 1000 male births, while XYY syndrome affects 1 in 1000 male births and Triple X syndrome affects 1 in 1000 births. Turner syndrome is less common, affecting 1 in 5000 female births. Edwards syndrome and Patau syndrome are rare, affecting 1 in 6000 and 1 in 10,000 births, respectively. Understanding the genetic basis and consequences of aneuploidy is important for diagnosis, treatment, and genetic counseling.
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This question is part of the following fields:
- Genetics
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Question 50
Incorrect
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Which inheritance pattern is not consistent with Mendelian genetics?
Your Answer:
Correct Answer: All are types of Mendelian inheritance
Explanation:The Law of Segregation and the Law of Independent Assortment are two fundamental principles of Mendelian inheritance. The Law of Segregation states that during gamete formation, the two alleles of a gene separate from each other so that each gamete receives only one allele. This means that offspring inherit one allele from each parent. The Law of Independent Assortment states that the inheritance of one gene does not affect the inheritance of another gene. This means that the alleles of different genes are distributed randomly into gametes. These laws are essential in understanding the inheritance patterns of single gene disorders. By following these laws, scientists can predict the likelihood of certain traits of disorders being passed down from one generation to the next.
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This question is part of the following fields:
- Genetics
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Question 51
Incorrect
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What is the protein that binds to undesired cellular proteins to mark them for breakdown by the proteasome?
Your Answer:
Correct Answer: Ubiquitin
Explanation:The Function of Proteasomes in Protein Degradation
Proteasomes play a crucial role in breaking down proteins that are produced within the cell. These cylindrical complexes are present in both the nucleus and cytoplasm of the cell. The process of protein degradation involves the tagging of proteins with a small protein called ubiquitin. The proteasome consists of a core structure made up of four stacked rings surrounding a central pore. Each ring is composed of seven individual proteins. This structure allows for the efficient degradation of proteins, ensuring that the cell can maintain proper protein levels and function.
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This question is part of the following fields:
- Genetics
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Question 52
Incorrect
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How many daughter cells are generated from the meiosis of a single parent cell?
Your Answer:
Correct Answer: 4
Explanation:Cytokinesis: The Final Stage of Cell Division
Cytokinesis is the final stage of cell division, where the cell splits into two daughter cells, each with a nucleus. This process is essential for the growth and repair of tissues in multicellular organisms. In mitosis, cytokinesis occurs after telophase, while in meiosis, it occurs after telophase I and telophase II.
During cytokinesis, a contractile ring made of actin and myosin filaments forms around the cell’s equator, constricting it like a belt. This ring gradually tightens, pulling the cell membrane inward and creating a furrow that deepens until it reaches the center of the cell. Eventually, the furrow meets in the middle, dividing the cell into two daughter cells.
In animal cells, cytokinesis is achieved by the formation of a cleavage furrow, while in plant cells, a cell plate forms between the two daughter nuclei, which eventually develops into a new cell wall. The timing and mechanism of cytokinesis are tightly regulated by a complex network of proteins and signaling pathways, ensuring that each daughter cell receives the correct amount of cytoplasm and organelles.
Overall, cytokinesis is a crucial step in the cell cycle, ensuring that genetic material is equally distributed between daughter cells and allowing for the growth and development of multicellular organisms.
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This question is part of the following fields:
- Genetics
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Question 53
Incorrect
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Which statement accurately describes Parkinson's disease?
Your Answer:
Correct Answer: Mutations in the gene that produces alpha-synuclein have been linked to early-onset Parkinson's disease
Explanation:Lewy bodies, which are present in Parkinson’s disease, are composed of alpha-synuclein.
Genetic Contributors to Parkinson’s Disease
Genetic contributors to Parkinson’s disease can range from highly penetrant DNA variants to variants that individually increase the lifetime risk of the disease. These genetic risks are often divided into rare DNA variants with high effect sizes, typically associated with familial Parkinson’s disease, and more common, smaller effect variants, usually identified in sporadic cases. While rare variants in over 20 genes have been reported to cause Parkinson’s disease, most cases are idiopathic.
One gene implicated in Parkinson’s disease is SNCA, which codes for alpha-synuclein. Autosomal dominant mutations of SNCA have been identified in several families with inherited Parkinson’s disease. Mutant forms of alpha-synuclein aggregate and induce other proteins to incorporate into the aggregate, forming Lewy bodies, which are similar to the beta-amyloid plaques found in Alzheimer’s patients. Another gene implicated in Parkinson’s disease is the Parkin gene.
It is important to note that the known genes responsible for Parkinson’s disease are responsible for a minority of cases, with the majority being sporadic.
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This question is part of the following fields:
- Genetics
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Question 54
Incorrect
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Which statement accurately describes ribonucleic acid (RNA)?
Your Answer:
Correct Answer: RNA is typically shorter than DNA
Explanation:Enzymes called RNA polymerases, not transferases, transcribe RNA from DNA.
Genomics: Understanding DNA, RNA, Transcription, and Translation
Deoxyribonucleic acid (DNA) is a molecule composed of two chains that coil around each other to form a double helix. DNA is organised into chromosomes, and each chromosome is made up of DNA coiled around proteins called histones. RNA, on the other hand, is made from a long chain of nucleotide units and is usually single-stranded. RNA is transcribed from DNA by enzymes called RNA polymerases and is central to protein synthesis.
Transcription is the synthesis of RNA from a DNA template, and it consists of three main steps: initiation, elongation, and termination. RNA polymerase binds at a sequence of DNA called the promoter, and the transcriptome is the collection of RNA molecules that results from transcription. Translation, on the other hand, refers to the synthesis of polypeptides (proteins) from mRNA. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.
The process of translation involves messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transfer RNAs, of tRNAs, connect mRNA codons to the amino acids they encode, while ribosomes are the structures where polypeptides (proteins) are built. Like transcription, translation also consists of three stages: initiation, elongation, and termination. In initiation, the ribosome assembles around the mRNA to be read and the first tRNA carrying the amino acid methionine. In elongation, the amino acid chain gets longer, and in termination, the finished polypeptide chain is released.
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This question is part of the following fields:
- Genetics
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Question 55
Incorrect
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What is the method used to identify the mode of inheritance for a particular trait?
Your Answer:
Correct Answer: Segregation analysis
Explanation:Segregation and Linkage Analysis in Genetics
In genetics, segregation analysis is a statistical approach that helps determine the mode of inheritance of a specific phenotype using family data. On the other hand, linkage analysis is a method used to identify the genetic location of a disease gene. The primary objective of linkage analysis is to find a piece of DNA that is inherited by all affected family members and not by any unaffected members. Once this DNA segment is identified, it indicates that the disease gene is located nearby. Both segregation and linkage analysis are crucial tools in genetic research, helping scientists understand the inheritance patterns of genetic traits and diseases. By using these methods, researchers can identify the genetic basis of various disorders and develop effective treatments.
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This question is part of the following fields:
- Genetics
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Question 56
Incorrect
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What is the rate of schizophrenia concordance among dizygotic twins according to the Gottesman data?
Your Answer:
Correct Answer: 17%
Explanation:Schizophrenia: A Genetic Disorder
Adoption studies have consistently shown that biological relatives of patients with schizophrenia have an increased risk of developing the disorder. Schizophrenia is a complex disorder with incomplete penetrance, as evidenced by the fact that monozygotic twins have a concordance rate of approximately 50%, while dizygotic twins have a concordance rate of 17%. This indicates a significant genetic contribution to the disorder, with an estimated heritability of 80%. Segregation analysis suggests that schizophrenia follows a multifactorial model.
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This question is part of the following fields:
- Genetics
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Question 57
Incorrect
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Which statement accurately describes aneuploidy?
Your Answer:
Correct Answer: Most aneuploidies result from the nondisjunction of chromosomes during meiosis I
Explanation:Aneuploidy: Abnormal Chromosome Numbers
Aneuploidy refers to the presence of an abnormal number of chromosomes, which can result from errors during meiosis. Typically, human cells have 23 pairs of chromosomes, but aneuploidy can lead to extra of missing chromosomes. Trisomies, which involve the presence of an additional chromosome, are the most common aneuploidies in humans. However, most trisomies are not compatible with life, and only trisomy 21 (Down’s syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) survive to birth. Aneuploidy can result in imbalances in gene expression, which can lead to a range of symptoms and developmental issues.
Compared to autosomal trisomies, humans are more able to tolerate extra sex chromosomes. Klinefelter’s syndrome, which involves the presence of an extra X chromosome, is the most common sex chromosome aneuploidy. Individuals with Klinefelter’s and XYY often remain undiagnosed, but they may experience reduced sexual development and fertility. Monosomies, which involve the loss of a chromosome, are rare in humans. The only viable human monosomy involves the X chromosome and results in Turner’s syndrome. Turner’s females display a wide range of symptoms, including infertility and impaired sexual development.
The frequency and severity of aneuploidies vary widely. Down’s syndrome is the most common viable autosomal trisomy, affecting 1 in 800 births. Klinefelter’s syndrome affects 1-2 in 1000 male births, while XYY syndrome affects 1 in 1000 male births and Triple X syndrome affects 1 in 1000 births. Turner syndrome is less common, affecting 1 in 5000 female births. Edwards syndrome and Patau syndrome are rare, affecting 1 in 6000 and 1 in 10,000 births, respectively. Understanding the genetic basis and consequences of aneuploidy is important for diagnosis, treatment, and genetic counseling.
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This question is part of the following fields:
- Genetics
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Question 58
Incorrect
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This means that 80% of the variation in ADHD can be attributed to genetic factors.
Your Answer:
Correct Answer: On average 80% of the variance of the condition in a population is due to genetic factors
Explanation:The heritability estimate does not provide any information about specific individuals.
Heritability: Understanding the Concept
Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.
The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:
Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.
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This question is part of the following fields:
- Genetics
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Question 59
Incorrect
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What is the name for an organism that develops from a single zygote but has multiple genetically distinct populations of cells?
Your Answer:
Correct Answer: Mosaic
Explanation:Understanding the Difference between Chimeras and Mosaics
Chimeras and mosaics are two types of animals that have multiple genetically distinct populations of cells. However, it is important to understand the clear distinction between these two forms, which is often ignored of misused.
Mosaics are animals that have different cell types that all originate from a single zygote. This means that during development, some cells may acquire genetic mutations of changes that make them different from the rest of the cells in the organism. These changes can occur randomly of due to environmental factors, and can result in different physical characteristics of traits within the same individual.
On the other hand, chimeras are animals that originate from more than one zygote. This can happen when two fertilized eggs fuse together early in development, of when two embryos merge into a single individual. As a result, chimeras have distinct populations of cells with different genetic makeups, which can lead to unique physical characteristics of traits.
A plasmid is an autonomously replicating, extrachromosomal circular DNA molecule, distinct from the normal bacterial genome and nonessential for cell survival under nonselective conditions. Some plasmids are capable of integrating into the host genome. A number of artificially constructed plasmids are used as cloning vectors.
A clone is an organism that is genetically identical to the unit of individual from which it was derived.
A morula is the term given to the spherical embryonic mass of blastomeres formed before the blastula and resulting from cleavage of the fertilized ovum. -
This question is part of the following fields:
- Genetics
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Question 60
Incorrect
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How does the presence of one APOE4 allele affect the risk of developing Alzheimer's dementia compared to not having any APOE4 allele?
Your Answer:
Correct Answer: 3
Explanation:Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 61
Incorrect
-
What is the term used to describe a segment of DNA that does not code for proteins and is not translated?
Your Answer:
Correct Answer: Intron
Explanation:Splicing of mRNA
After the transcription of DNA into mRNA, the mRNA undergoes a crucial process known as splicing. This process involves the removal of certain portions of the mRNA, called introns, leaving behind the remaining portions known as exons. The exons are then translated into proteins. The resulting spliced form of RNA is referred to as mature mRNA. This process of splicing is essential for the proper functioning of genes and the production of functional proteins.
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This question is part of the following fields:
- Genetics
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Question 62
Incorrect
-
Which syndrome is also referred to as Trisomy 18?
Your Answer:
Correct Answer: Edward's syndrome
Explanation:Aneuploidy: Abnormal Chromosome Numbers
Aneuploidy refers to the presence of an abnormal number of chromosomes, which can result from errors during meiosis. Typically, human cells have 23 pairs of chromosomes, but aneuploidy can lead to extra of missing chromosomes. Trisomies, which involve the presence of an additional chromosome, are the most common aneuploidies in humans. However, most trisomies are not compatible with life, and only trisomy 21 (Down’s syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) survive to birth. Aneuploidy can result in imbalances in gene expression, which can lead to a range of symptoms and developmental issues.
Compared to autosomal trisomies, humans are more able to tolerate extra sex chromosomes. Klinefelter’s syndrome, which involves the presence of an extra X chromosome, is the most common sex chromosome aneuploidy. Individuals with Klinefelter’s and XYY often remain undiagnosed, but they may experience reduced sexual development and fertility. Monosomies, which involve the loss of a chromosome, are rare in humans. The only viable human monosomy involves the X chromosome and results in Turner’s syndrome. Turner’s females display a wide range of symptoms, including infertility and impaired sexual development.
The frequency and severity of aneuploidies vary widely. Down’s syndrome is the most common viable autosomal trisomy, affecting 1 in 800 births. Klinefelter’s syndrome affects 1-2 in 1000 male births, while XYY syndrome affects 1 in 1000 male births and Triple X syndrome affects 1 in 1000 births. Turner syndrome is less common, affecting 1 in 5000 female births. Edwards syndrome and Patau syndrome are rare, affecting 1 in 6000 and 1 in 10,000 births, respectively. Understanding the genetic basis and consequences of aneuploidy is important for diagnosis, treatment, and genetic counseling.
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This question is part of the following fields:
- Genetics
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Question 63
Incorrect
-
What is the correct statement about the recombination fraction?
Your Answer:
Correct Answer: It is a measure of the distance between two loci
Explanation:Recombination Fraction: A Measure of Distance Between Loci
When two loci are located on different chromosomes, they segregate independently during meiosis. However, if they are on the same chromosome, they tend to segregate together, unless crossing over occurs. Crossing over is a process in meiosis where two homologous chromosomes exchange genetic material, resulting in the shuffling of alleles. The likelihood of crossing over between two loci on a chromosome decreases as their distance from each other increases.
Hence, blocks of alleles on a chromosome tend to be transmitted together through generations, forming a haplotype. The recombination fraction is a measure of the distance between two loci on a chromosome. The closer the loci are, the lower the recombination fraction, and the more likely they are to be transmitted together. Conversely, the further apart the loci are, the higher the recombination fraction, and the more likely they are to be separated by crossing over. The recombination fraction can range from 0% if the loci are very close to 50% if they are on different chromosomes.
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This question is part of the following fields:
- Genetics
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Question 64
Incorrect
-
Is the following estimate of heritability accurate?
Your Answer:
Correct Answer: Major depression = 30%
Explanation:Heritability: Understanding the Concept
Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.
The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:
Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.
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This question is part of the following fields:
- Genetics
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Question 65
Incorrect
-
What is the most frequently occurring genetic mutation in individuals with early onset familial Alzheimer's disease?
Your Answer:
Correct Answer: PSEN1
Explanation:Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 66
Incorrect
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How would you describe a group of DNA variations that are commonly passed down together?
Your Answer:
Correct Answer: Haplotype
Explanation:Inheritance: Phenotype and Genotype
Phenotype refers to the observable traits of an individual, such as height, eye colour, and blood type. These traits are a result of the interaction between an individual’s genotype and the environment. The term ‘pheno’ comes from the same root as ‘phenomenon’ and simply means ‘observe’.
On the other hand, genotype refers to an individual’s collection of genes. These genes determine the traits that an individual will inherit from their parents. A haplotype, on the other hand, is a set of DNA variations of polymorphisms that tend to be inherited together.
Finally, a karyotype refers to an individual’s collection of chromosomes. These chromosomes contain the genetic information that determines an individual’s traits. By examining an individual’s karyotype, scientists can determine if there are any genetic abnormalities of disorders present.
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This question is part of the following fields:
- Genetics
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Question 67
Incorrect
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Which condition is marked by an increased appetite and being overweight?
Your Answer:
Correct Answer: Prader-Willi syndrome
Explanation:Prader-Willi Syndrome: A Genetic Disorder with Unique Characteristics
Prader-Willi Syndrome is a genetic disorder that occurs when there is a deletion of genetic material from the paternal chromosome 15. This condition is a classic example of imprinting, where the expression of certain genes is dependent on whether they are inherited from the mother of father. The syndrome is characterized by several unique features, including hyperphagia (excessive eating) and obesity, short stature, delayed puberty, hypogonadism, infertility, learning difficulties, and compulsive behavior such as skin picking.
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This question is part of the following fields:
- Genetics
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Question 68
Incorrect
-
What condition primarily impacts females?
Your Answer:
Correct Answer: Rett syndrome
Explanation:Genetic Conditions and Their Features
Genetic conditions are disorders caused by abnormalities in an individual’s DNA. These conditions can affect various aspects of a person’s health, including physical and intellectual development. Some of the most common genetic conditions and their features are:
– Downs (trisomy 21): Short stature, almond-shaped eyes, low muscle tone, and intellectual disability.
– Angelman syndrome (Happy puppet syndrome): Flapping hand movements, ataxia, severe learning disability, seizures, and sleep problems.
– Prader-Willi: Hyperphagia, excessive weight gain, short stature, and mild learning disability.
– Cri du chat: Characteristic cry, hypotonia, down-turned mouth, and microcephaly.
– Velocardiofacial syndrome (DiGeorge syndrome): Cleft palate, cardiac problems, and learning disabilities.
– Edwards syndrome (trisomy 18): Severe intellectual disability, kidney malformations, and physical abnormalities.
– Lesch-Nyhan syndrome: Self-mutilation, dystonia, and writhing movements.
– Smith-Magenis syndrome: Pronounced self-injurious behavior, self-hugging, and a hoarse voice.
– Fragile X: Elongated face, large ears, hand flapping, and shyness.
– Wolf Hirschhorn syndrome: Mild to severe intellectual disability, seizures, and physical abnormalities.
– Patau syndrome (trisomy 13): Severe intellectual disability, congenital heart malformations, and physical abnormalities.
– Rett syndrome: Regression and loss of skills, hand-wringing movements, and profound learning disability.
– Tuberous sclerosis: Hamartomatous tumors, epilepsy, and behavioral issues.
– Williams syndrome: Elfin-like features, social disinhibition, and advanced verbal skills.
– Rubinstein-Taybi syndrome: Short stature, friendly disposition, and moderate learning disability.
– Klinefelter syndrome: Extra X chromosome, low testosterone, and speech and language issues.
– Jakob’s syndrome: Extra Y chromosome, tall stature, and lower mean intelligence.
– Coffin-Lowry syndrome: Short stature, slanting eyes, and severe learning difficulty.
– Turner syndrome: Short stature, webbed neck, and absent periods.
– Niemann Pick disease (types A and B): Abdominal swelling, cherry red spot, and feeding difficulties.It is important to note that these features may vary widely among individuals with the same genetic condition. Early diagnosis and intervention can help individuals with genetic conditions reach their full potential and improve their quality of life.
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This question is part of the following fields:
- Genetics
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Question 69
Incorrect
-
What is the estimated degree of genetic influence on autism?
Your Answer:
Correct Answer: 70%
Explanation:Heritability: Understanding the Concept
Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.
The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:
Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.
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This question is part of the following fields:
- Genetics
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Question 70
Incorrect
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What is the truth about the genetics of dementia?
Your Answer:
Correct Answer: CADASIL follows an autosomal dominant inheritance pattern
Explanation:Genes Associated with Dementia
Dementia is a complex disorder that can be caused by various genetic and environmental factors. Several genes have been implicated in different forms of dementia. For instance, familial Alzheimer’s disease, which represents less than 1-6% of all Alzheimer’s cases, is associated with mutations in PSEN1, PSEN2, APP, and ApoE genes. These mutations are inherited in an autosomal dominant pattern. On the other hand, late-onset Alzheimer’s disease is a genetic risk factor associated with the ApoE gene, particularly the APOE4 allele. However, inheriting this allele does not necessarily mean that a person will develop Alzheimer’s.
Other forms of dementia, such as familial frontotemporal dementia, Huntington’s disease, CADASIL, and dementia with Lewy bodies, are also associated with specific genes. For example, C9orf72 is the most common mutation associated with familial frontotemporal dementia, while Huntington’s disease is caused by mutations in the HTT gene. CADASIL is associated with mutations in the Notch3 gene, while dementia with Lewy bodies is associated with the APOE, GBA, and SNCA genes.
In summary, understanding the genetic basis of dementia is crucial for developing effective treatments and preventive measures. However, it is important to note that genetics is only one of the many factors that contribute to the development of dementia. Environmental factors, lifestyle choices, and other health conditions also play a significant role.
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This question is part of the following fields:
- Genetics
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Question 71
Incorrect
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What is the closest estimate of heritability in bipolar disorder?
Your Answer:
Correct Answer: 50%
Explanation:Heritability: Understanding the Concept
Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.
The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:
Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.
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This question is part of the following fields:
- Genetics
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Question 72
Incorrect
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Which statement accurately describes Prader-Willi syndrome?
Your Answer:
Correct Answer: Affected individuals typically have small gonads
Explanation:Genomic Imprinting and its Role in Psychiatric Disorders
Genomic imprinting is a phenomenon where a piece of DNA behaves differently depending on whether it is inherited from the mother of the father. This is because DNA sequences are marked of imprinted in the ovaries and testes, which affects their expression. In psychiatry, two classic examples of genomic imprinting disorders are Prader-Willi and Angelman syndrome.
Prader-Willi syndrome is caused by a deletion of chromosome 15q when inherited from the father. This disorder is characterized by hypotonia, short stature, polyphagia, obesity, small gonads, and mild mental retardation. On the other hand, Angelman syndrome, also known as Happy Puppet syndrome, is caused by a deletion of 15q when inherited from the mother. This disorder is characterized by an unusually happy demeanor, developmental delay, seizures, sleep disturbance, and jerky hand movements.
Overall, genomic imprinting plays a crucial role in the development of psychiatric disorders. Understanding the mechanisms behind genomic imprinting can help in the diagnosis and treatment of these disorders.
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This question is part of the following fields:
- Genetics
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Question 73
Incorrect
-
Which enzyme is believed to play a role in the likelihood of developing alcohol addiction?
Your Answer:
Correct Answer: Aldehyde dehydrogenase
Explanation:Functional polymorphisms in two alcohol dehydrogenase genes (ADHIB and ADH1C on chromosome 4) and one aldehyde dehydrogenase gene (ALDH2 on chromosome 12) have been linked to lower rates of alcohol dependence. The strongest association is with the ALDH2*2 allele, which is almost exclusively found in Asian populations. Other alleles, such as ADH1B*2, ADH1B*3, and ADHlC*i, found in varying prevalence in different ethnic groups, have also been associated with lower rates of alcohol dependence.
The proposed mechanism for these associations is that the isoenzymes encoded by these alleles lead to an accumulation of acetaldehyde during alcohol metabolism. ALDH2*2 theoretically leads to a slower removal of acetaldehyde than ALDH2*1, while ADH1B*2 and ADH1B*3 lead to a more rapid production of acetaldehyde than ADHIB*I. It is believed that higher levels of acetaldehyde cause more intense reactions to alcohol and lead to lower levels of alcohol intake.
Genetics and Alcoholism
Alcoholism tends to run in families, and several studies confirm that biological children of alcoholics are more likely to develop alcoholism even when adopted by parents without the condition. Monozygotic twins have a greater concordance rate for alcoholism than dizygotic twins. Heritability estimates range from 45 to 65 percent for both men and women. While genetic differences affect risk, there is no “gene for alcoholism,” and both environmental and social factors weigh heavily on the outcome.
The genes with the clearest contribution to the risk for alcoholism and alcohol consumption are alcohol dehydrogenase 1B (ADH1B) and aldehyde dehydrogenase 2 (ALDH2). The first step in ethanol metabolism is oxidation to acetaldehyde, by ADHs. The second step is metabolism of the acetaldehyde to acetate by ALDHs. Individuals carrying even a single copy of the ALDH2*504K display the “Asian flushing reaction” when they consume even small amounts of alcohol. There is one significant genetic polymorphism of the ALDH2 gene, resulting in allelic variants ALDH2*1 and ALDH2*2, which is virtually inactive. ALDH2*2 is present in about 50 percent of the Taiwanese, Han Chinese, and Japanese populations. It is extremely rare outside Asia. Nearly no individuals of European of African descent carry this allele. ALDH2*504K has repeatedly been demonstrated to have a protective effect against alcohol use disorders.
The three different class I gene loci, ADH1A (alpha), ADH1B (beta), and ADH1C (gamma) are situated close to each other in the region 4q2123. The alleles ADH1C*1 and ADH1B*2 code for fast metabolism of alcohol. The ADH1B*1 slow allele is very common among Caucasians, with approximately 95 percent having the homozygous ADH1B*1/1 genotype and 5 percent having the heterozygous ADH1B*1/2 genotype. The ADH1B*2 allele is the most common allele in Asian populations. In African populations, the ADH1B*1 allele is the most common.
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This question is part of the following fields:
- Genetics
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Question 74
Incorrect
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Which of the following is characterized by cluttered speech?
Your Answer:
Correct Answer: Fragile X syndrome
Explanation:Fragile X is associated with speech that is cluttered.
Fragile X Syndrome: A Genetic Disorder Causing Learning Disability and Psychiatric Symptoms
Fragile X Syndrome is a genetic disorder that causes mental retardation, an elongated face, large protruding ears, and large testicles in men. Individuals with this syndrome tend to be shy, avoid eye contact, and have difficulties reading facial expressions. They also display stereotypic movements such as hand flapping. Fragile X Syndrome is the most common inherited cause of learning disability.
The speech of affected individuals is often abnormal, with abnormalities of fluency. This disorder is caused by the amplification of a CGG repeat in the 5 untranslated region of the fragile X mental retardation 1 gene (FMR1). These CGG repeats disrupt synthesis of the fragile X protein (FMRP), which is essential for brain function and growth. The gene is located at Xq27. The greater number of repeats, the more severe the condition, as with other trinucleotide repeat disorders.
The fragile X phenotype typically involves a variety of psychiatric symptoms, including features of autism, attention deficit/hyperactivity disorder, anxiety, and aggression. Both males and females can be affected, but males are more severely affected because they have only one X chromosome. The prevalence estimate of Fragile X Syndrome is 1/3600-4000.
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This question is part of the following fields:
- Genetics
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Question 75
Incorrect
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Which of the following candidate genes for schizophrenia is located on chromosome 6?
Your Answer:
Correct Answer: DTNBP1
Explanation:Schizophrenia is a complex disorder that is associated with multiple candidate genes. No single gene has been identified as the sole cause of schizophrenia, and it is believed that the more genes involved, the greater the risk. Some of the important candidate genes for schizophrenia include DTNBP1, COMT, NRG1, G72, RGS4, DAOA, DISC1, and DRD2. Among these, neuregulin, dysbindin, and DISC1 are the most replicated and plausible genes, with COMT being the strongest candidate gene due to its role in dopamine metabolism. Low activity of the COMT gene has been associated with obsessive-compulsive disorder and schizophrenia. Neuregulin 1 is a growth factor that stimulates neuron development and differentiation, and increased neuregulin signaling in schizophrenia may suppress the NMDA receptor, leading to lowered glutamate levels. Dysbindin is involved in the biogenesis of lysosome-related organelles, and its expression is decreased in schizophrenia. DISC1 encodes a multifunctional protein that influences neuronal development and adult brain function, and it is disrupted in schizophrenia. It is located at the breakpoint of a balanced translocation identified in a large Scottish family with schizophrenia, schizoaffective disorder, and other major mental illnesses.
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This question is part of the following fields:
- Genetics
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Question 76
Incorrect
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How can the mode of inheritance that exhibits knights move inheritance be described?
Your Answer:
Correct Answer: X-linked recessive
Explanation:Inheritance of knight’s move pattern is observed in disorders that are caused by recessive X-linked genes, rather than dominant X-linked genes.
Modes of Inheritance
Genetic disorders can be passed down from one generation to the next in various ways. There are four main modes of inheritance: autosomal dominant, autosomal recessive, X-linked (sex-linked), and multifactorial.
Autosomal Dominant Inheritance
Autosomal dominant inheritance occurs when one faulty gene causes a problem despite the presence of a normal one. This type of inheritance shows vertical transmission, meaning it is based on the appearance of the family pedigree. If only one parent is affected, there is a 50% chance of each child expressing the condition. Autosomal dominant conditions often show pleiotropy, where a single gene influences several characteristics.
Autosomal Recessive Inheritance
In autosomal recessive conditions, a person requires two faulty copies of a gene to manifest a disease. A person with one healthy and one faulty gene will generally not manifest a disease and is labelled a carrier. Autosomal recessive conditions demonstrate horizontal transmission.
X-linked (Sex-linked) Inheritance
In X-linked conditions, the problem gene lies on the X chromosome. This means that all males are affected. Like autosomal conditions, they can be dominant of recessive. Affected males are unable to pass the condition on to their sons. In X-linked recessive conditions, the inheritance pattern is characterised by transmission from affected males to male grandchildren via affected carrier daughters.
Multifactorial Inheritance
Multifactorial conditions result from the interaction between genes from both parents and the environment.
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This question is part of the following fields:
- Genetics
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Question 77
Incorrect
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What is the characteristic feature of EEG in individuals with Huntington's disease?
Your Answer:
Correct Answer: Shows a flattened trace
Explanation:Huntington’s Disease: Genetics and Pathology
Huntington’s disease is a genetic disorder that follows an autosomal dominant pattern of inheritance. It is caused by a mutation in the Huntington gene, which is located on chromosome 4. The mutation involves an abnormal expansion of a trinucleotide repeat sequence (CAG), which leads to the production of a toxic protein that damages brain cells.
The severity of the disease and the age of onset are related to the number of CAG repeats. Normally, the CAG sequence is repeated less than 27 times, but in Huntington’s disease, it is repeated many more times. The disease shows anticipation, meaning that it tends to worsen with each successive generation.
The symptoms of Huntington’s disease typically begin in the third of fourth decade of life, but in rare cases, they can appear in childhood of adolescence. The most common symptoms include involuntary movements (chorea), cognitive decline, and psychiatric disturbances.
The pathological hallmark of Huntington’s disease is the gross bilateral atrophy of the head of the caudate and putamen, which are regions of the brain involved in movement control. The EEG of patients with Huntington’s disease shows a flattened trace, indicating a loss of brain activity.
Macroscopic pathological findings include frontal atrophy, marked atrophy of the caudate and putamen, and enlarged ventricles. Microscopic findings include neuronal loss and gliosis in the cortex, neuronal loss in the striatum, and the presence of inclusion bodies in the neurons of the cortex and striatum.
In conclusion, Huntington’s disease is a devastating genetic disorder that affects the brain and causes a range of motor, cognitive, and psychiatric symptoms. The disease is caused by a mutation in the Huntington gene, which leads to the production of a toxic protein that damages brain cells. The pathological changes in the brain include atrophy of the caudate and putamen, neuronal loss, and the presence of inclusion bodies.
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This question is part of the following fields:
- Genetics
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Question 78
Incorrect
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What is the most appropriate term to describe the process by which one gene can generate multiple variations of proteins?
Your Answer:
Correct Answer: Alternative splicing
Explanation:Alternative splicing is a crucial process in post-transcriptional processing that has significant implications. It allows a single gene to produce multiple mRNAs that encode different polypeptides by modifying the splicing pattern. However, mutations in the gene sequence can lead to either a lack of splicing of excessive splicing, resulting in diseases.
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This question is part of the following fields:
- Genetics
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Question 79
Incorrect
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From which region of genetic material is deleted in Angelman syndrome?
Your Answer:
Correct Answer: Chromosome 15
Explanation:Genomic Imprinting and its Role in Psychiatric Disorders
Genomic imprinting is a phenomenon where a piece of DNA behaves differently depending on whether it is inherited from the mother of the father. This is because DNA sequences are marked of imprinted in the ovaries and testes, which affects their expression. In psychiatry, two classic examples of genomic imprinting disorders are Prader-Willi and Angelman syndrome.
Prader-Willi syndrome is caused by a deletion of chromosome 15q when inherited from the father. This disorder is characterized by hypotonia, short stature, polyphagia, obesity, small gonads, and mild mental retardation. On the other hand, Angelman syndrome, also known as Happy Puppet syndrome, is caused by a deletion of 15q when inherited from the mother. This disorder is characterized by an unusually happy demeanor, developmental delay, seizures, sleep disturbance, and jerky hand movements.
Overall, genomic imprinting plays a crucial role in the development of psychiatric disorders. Understanding the mechanisms behind genomic imprinting can help in the diagnosis and treatment of these disorders.
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This question is part of the following fields:
- Genetics
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Question 80
Incorrect
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What is the pattern of inheritance where female offspring of affected fathers do not exhibit symptoms of carry the genetic mutation?
Your Answer:
Correct Answer: Y-linked
Explanation:Inheritance Patterns:
Autosomal Dominant Conditions:
– Can be transmitted from one generation to the next (vertical transmission) through all forms of transmission observed (male to male, male to female, female to female).
– Males and females are affected in equal proportions.
– Usually, one parent is an affected heterozygote and the other is an unaffected homozygote.
– If only one parent is affected, there is a 50% chance that a child will inherit the mutated gene.Autosomal Recessive Conditions:
– Males and females are affected in equal proportions.
– Two copies of the gene must be mutated for a person to be affected.
– Both parents are usually unaffected heterozygotes.
– Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder.X-linked Dominant Conditions:
– Males and females are both affected, with males typically being more severely affected than females.
– The sons of a man with an X-linked dominant disorder will all be unaffected.
– A woman with an X-linked dominant disorder has a 50% chance of having an affected fetus.X-linked Recessive Conditions:
– Males are more frequently affected than females.
– Transmitted through carrier females to their sons (knights move pattern).
– Affected males cannot pass the condition onto their sons.
– A woman who is a carrier of an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers.Y-linked Conditions:
– Every son of an affected father will be affected.
– Female offspring of affected fathers are never affected.Mitochondrial Inheritance:
– Mitochondria are inherited only in the maternal ova and not in sperm.
– Males and females are affected, but always being maternally inherited.
– An affected male does not pass on his mitochondria to his children, so all his children will be unaffected. -
This question is part of the following fields:
- Genetics
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Question 81
Incorrect
-
Which condition has the highest estimate of heritability among the options provided?
Your Answer:
Correct Answer: Schizophrenia
Explanation:Heritability: Understanding the Concept
Heritability is a concept that is often misunderstood. It is not a measure of the extent to which genes cause a condition in an individual. Rather, it is the proportion of phenotypic variance attributable to genetic variance. In other words, it tells us how much of the variation in a condition seen in a population is due to genetic factors. Heritability is calculated using statistical techniques and can range from 0.0 to 1.0. For human behavior, most estimates of heritability fall in the moderate range of .30 to .60.
The quantity (1.0 – heritability) gives the environment ability of the trait. This is the proportion of phenotypic variance attributable to environmental variance. The following table provides estimates of heritability for major conditions:
Condition Heritability estimate (approx)
ADHD 85%
Autism 70%
Schizophrenia 55%
Bipolar 55%
Anorexia 35%
Alcohol dependence 35%
Major depression 30%
OCD 25%It is important to note that heritability tells us nothing about individuals. It is a population-level measure that helps us understand the relative contributions of genetic and environmental factors to a particular condition.
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This question is part of the following fields:
- Genetics
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Question 82
Incorrect
-
Is macrocephaly associated with Fragile X syndrome?
Your Answer:
Correct Answer: Fragile X syndrome
Explanation:Macrocephaly is a characteristic often seen in individuals with Fragile X syndrome.
Microcephaly: A Condition of Small Head Size
Microcephaly is a condition characterized by a small head size. It can be a feature of various conditions, including fetal alcohol syndrome, Down’s syndrome, Edward’s syndrome, Patau syndrome, Angelman syndrome, De Lange syndrome, Prader-Willi syndrome, and Cri-du-chat syndrome. Each of these conditions has its own unique set of symptoms and causes, but they all share the common feature of microcephaly. This condition can have a range of effects on a person’s development, including intellectual disability, seizures, and motor problems. Early diagnosis and intervention can help manage the symptoms and improve outcomes for individuals with microcephaly.
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This question is part of the following fields:
- Genetics
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Question 83
Incorrect
-
What traits of conditions can be passed down through autosomal dominant inheritance?
Your Answer:
Correct Answer: Velocardiofacial syndrome
Explanation:Inheritance Patterns and Examples
Autosomal Dominant:
Neurofibromatosis type 1 and 2, tuberous sclerosis, achondroplasia, Huntington disease, and Noonan’s syndrome are all examples of conditions that follow an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene is needed to cause the condition.Autosomal Recessive:
Phenylketonuria, homocystinuria, Hurler’s syndrome, galactosaemia, Tay-Sach’s disease, Friedreich’s ataxia, Wilson’s disease, and cystic fibrosis are all examples of conditions that follow an autosomal recessive inheritance pattern. This means that two copies of the mutated gene are needed to cause the condition.X-Linked Dominant:
Vitamin D resistant rickets and Rett syndrome are examples of conditions that follow an X-linked dominant inheritance pattern. This means that the mutated gene is located on the X chromosome and only one copy of the gene is needed to cause the condition.X-Linked Recessive:
Cerebellar ataxia, Hunter’s syndrome, and Lesch-Nyhan are examples of conditions that follow an X-linked recessive inheritance pattern. This means that the mutated gene is located on the X chromosome and two copies of the gene are needed to cause the condition.Mitochondrial:
Leber’s hereditary optic neuropathy and Kearns-Sayre syndrome are examples of conditions that follow a mitochondrial inheritance pattern. This means that the mutated gene is located in the mitochondria and is passed down from the mother to her offspring. -
This question is part of the following fields:
- Genetics
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Question 84
Incorrect
-
What is the probability of an offspring being an asymptomatic carrier if both parents are heterozygous for an autosomal recessive trait?
Your Answer:
Correct Answer: 50%
Explanation:When two individuals who are heterozygous for an autosomal recessive condition have a child, there is a 25% chance that the child will be affected by the condition, a 50% chance that the child will be a carrier of the condition but not show any symptoms, and a 25% chance that the child will not carry the condition and will be completely normal.
Inheritance Patterns:
Autosomal Dominant Conditions:
– Can be transmitted from one generation to the next (vertical transmission) through all forms of transmission observed (male to male, male to female, female to female).
– Males and females are affected in equal proportions.
– Usually, one parent is an affected heterozygote and the other is an unaffected homozygote.
– If only one parent is affected, there is a 50% chance that a child will inherit the mutated gene.Autosomal Recessive Conditions:
– Males and females are affected in equal proportions.
– Two copies of the gene must be mutated for a person to be affected.
– Both parents are usually unaffected heterozygotes.
– Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder.X-linked Dominant Conditions:
– Males and females are both affected, with males typically being more severely affected than females.
– The sons of a man with an X-linked dominant disorder will all be unaffected.
– A woman with an X-linked dominant disorder has a 50% chance of having an affected fetus.X-linked Recessive Conditions:
– Males are more frequently affected than females.
– Transmitted through carrier females to their sons (knights move pattern).
– Affected males cannot pass the condition onto their sons.
– A woman who is a carrier of an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers.Y-linked Conditions:
– Every son of an affected father will be affected.
– Female offspring of affected fathers are never affected.Mitochondrial Inheritance:
– Mitochondria are inherited only in the maternal ova and not in sperm.
– Males and females are affected, but always being maternally inherited.
– An affected male does not pass on his mitochondria to his children, so all his children will be unaffected. -
This question is part of the following fields:
- Genetics
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Question 85
Incorrect
-
What is the term used to refer to individuals with a certain chromosomal abnormality as super-males?
Your Answer:
Correct Answer: 47 XYY
Explanation:XYY Syndrome
XYY Syndrome, also known as Jacobs’ Syndrome of super-males, is a genetic condition where males have an extra Y chromosome, resulting in a 47, XYY karyotype. In some cases, mosaicism may occur, resulting in a 47,XYY/46,XY karyotype. The error leading to the 47,XYY genotype occurs during spermatogenesis of post-zygotic mitosis. The prevalence of XYY Syndrome is as high as 1:1000 male live births, but many cases go unidentified as they are not necessarily associated with physical of cognitive impairments. The most common features are high stature and a strong build, and fertility and sexual development are usually unaffected. In the past, XYY Syndrome was linked to aggressiveness and deviance, but this is likely due to intermediate factors such as reduced IQ and social deprivation. XYY Syndrome is best thought of as a risk factor rather than a cause. There is an increased risk of developmental disorders such as learning difficulties, ASD, ADHD, and emotional problems.
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This question is part of the following fields:
- Genetics
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Question 86
Incorrect
-
Which statement about Williams syndrome is not true?
Your Answer:
Correct Answer: It results from a microdeletion in chromosome 8
Explanation:Understanding Williams Syndrome
Williams syndrome is a rare neurodevelopmental disorder that is characterized by distinct physical and behavioral traits. Individuals with this syndrome have a unique facial appearance, including a low nasal bridge and a cheerful demeanor. They also tend to have mild to moderate mental retardation and are highly sociable and verbal.
Children with Williams syndrome are particularly sensitive to sound and may overreact to loud of high-pitched noises. The syndrome is caused by a deletion in the q11.23 region of chromosome 7, which codes for more than 20 genes. This deletion typically occurs during the recombination phase of meiosis and can be detected using fluorescent in situ hybridization (FISH).
Although Williams syndrome is an autosomal dominant condition, most cases are not inherited and occur sporadically in individuals with no family history of the disorder. With a prevalence of around 1 in 20,000, Williams syndrome is a rare condition that requires specialized care and support.
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This question is part of the following fields:
- Genetics
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Question 87
Incorrect
-
What is true about the genetics of alcoholism?
Your Answer:
Correct Answer: The heritability of alcohol dependence is thought to be between 45-65%
Explanation:Genetics and Alcoholism
Alcoholism tends to run in families, and several studies confirm that biological children of alcoholics are more likely to develop alcoholism even when adopted by parents without the condition. Monozygotic twins have a greater concordance rate for alcoholism than dizygotic twins. Heritability estimates range from 45 to 65 percent for both men and women. While genetic differences affect risk, there is no “gene for alcoholism,” and both environmental and social factors weigh heavily on the outcome.
The genes with the clearest contribution to the risk for alcoholism and alcohol consumption are alcohol dehydrogenase 1B (ADH1B) and aldehyde dehydrogenase 2 (ALDH2). The first step in ethanol metabolism is oxidation to acetaldehyde, by ADHs. The second step is metabolism of the acetaldehyde to acetate by ALDHs. Individuals carrying even a single copy of the ALDH2*504K display the “Asian flushing reaction” when they consume even small amounts of alcohol. There is one significant genetic polymorphism of the ALDH2 gene, resulting in allelic variants ALDH2*1 and ALDH2*2, which is virtually inactive. ALDH2*2 is present in about 50 percent of the Taiwanese, Han Chinese, and Japanese populations. It is extremely rare outside Asia. Nearly no individuals of European of African descent carry this allele. ALDH2*504K has repeatedly been demonstrated to have a protective effect against alcohol use disorders.
The three different class I gene loci, ADH1A (alpha), ADH1B (beta), and ADH1C (gamma) are situated close to each other in the region 4q2123. The alleles ADH1C*1 and ADH1B*2 code for fast metabolism of alcohol. The ADH1B*1 slow allele is very common among Caucasians, with approximately 95 percent having the homozygous ADH1B*1/1 genotype and 5 percent having the heterozygous ADH1B*1/2 genotype. The ADH1B*2 allele is the most common allele in Asian populations. In African populations, the ADH1B*1 allele is the most common.
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This question is part of the following fields:
- Genetics
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Question 88
Incorrect
-
On which chromosome is the candidate gene for schizophrenia that codes for the Catechol-O-Methyltransferase enzyme located?
Your Answer:
Correct Answer: 22
Explanation:Schizophrenia is a complex disorder that is associated with multiple candidate genes. No single gene has been identified as the sole cause of schizophrenia, and it is believed that the more genes involved, the greater the risk. Some of the important candidate genes for schizophrenia include DTNBP1, COMT, NRG1, G72, RGS4, DAOA, DISC1, and DRD2. Among these, neuregulin, dysbindin, and DISC1 are the most replicated and plausible genes, with COMT being the strongest candidate gene due to its role in dopamine metabolism. Low activity of the COMT gene has been associated with obsessive-compulsive disorder and schizophrenia. Neuregulin 1 is a growth factor that stimulates neuron development and differentiation, and increased neuregulin signaling in schizophrenia may suppress the NMDA receptor, leading to lowered glutamate levels. Dysbindin is involved in the biogenesis of lysosome-related organelles, and its expression is decreased in schizophrenia. DISC1 encodes a multifunctional protein that influences neuronal development and adult brain function, and it is disrupted in schizophrenia. It is located at the breakpoint of a balanced translocation identified in a large Scottish family with schizophrenia, schizoaffective disorder, and other major mental illnesses.
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This question is part of the following fields:
- Genetics
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Question 89
Incorrect
-
In which phase does the process of genetic recombination occur?
Your Answer:
Correct Answer: Prophase I
Explanation:Cytokinesis: The Final Stage of Cell Division
Cytokinesis is the final stage of cell division, where the cell splits into two daughter cells, each with a nucleus. This process is essential for the growth and repair of tissues in multicellular organisms. In mitosis, cytokinesis occurs after telophase, while in meiosis, it occurs after telophase I and telophase II.
During cytokinesis, a contractile ring made of actin and myosin filaments forms around the cell’s equator, constricting it like a belt. This ring gradually tightens, pulling the cell membrane inward and creating a furrow that deepens until it reaches the center of the cell. Eventually, the furrow meets in the middle, dividing the cell into two daughter cells.
In animal cells, cytokinesis is achieved by the formation of a cleavage furrow, while in plant cells, a cell plate forms between the two daughter nuclei, which eventually develops into a new cell wall. The timing and mechanism of cytokinesis are tightly regulated by a complex network of proteins and signaling pathways, ensuring that each daughter cell receives the correct amount of cytoplasm and organelles.
Overall, cytokinesis is a crucial step in the cell cycle, ensuring that genetic material is equally distributed between daughter cells and allowing for the growth and development of multicellular organisms.
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This question is part of the following fields:
- Genetics
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Question 90
Incorrect
-
What is the likelihood of a child developing schizophrenia if one of their parents has the condition, based on the Gottesman data?
Your Answer:
Correct Answer: 13%
Explanation:Schizophrenia Risk According to Gottesman
Irving I. Gottesman conducted family and twin studies in European populations between 1920 and 1987 to determine the risk of developing schizophrenia for relatives of those with the disorder. The following table displays Gottesman’s findings, which show the average lifetime risk for each relationship:
General population: 1%
First cousin: 2%
Uncle/aunt: 2%
Nephew/niece: 4%
Grandchildren: 5%
Parents: 6%
Half sibling: 6%
Full sibling: 9%
Children: 13%
Fraternal twins: 17%
Offspring of dual matings (both parents had schizophrenia): 46%
Identical twins: 48% -
This question is part of the following fields:
- Genetics
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Question 91
Incorrect
-
Select the correct order of the phases in the cell cycle:
Your Answer:
Correct Answer: G1, S phase, G2, mitosis
Explanation:Cytokinesis: The Final Stage of Cell Division
Cytokinesis is the final stage of cell division, where the cell splits into two daughter cells, each with a nucleus. This process is essential for the growth and repair of tissues in multicellular organisms. In mitosis, cytokinesis occurs after telophase, while in meiosis, it occurs after telophase I and telophase II.
During cytokinesis, a contractile ring made of actin and myosin filaments forms around the cell’s equator, constricting it like a belt. This ring gradually tightens, pulling the cell membrane inward and creating a furrow that deepens until it reaches the center of the cell. Eventually, the furrow meets in the middle, dividing the cell into two daughter cells.
In animal cells, cytokinesis is achieved by the formation of a cleavage furrow, while in plant cells, a cell plate forms between the two daughter nuclei, which eventually develops into a new cell wall. The timing and mechanism of cytokinesis are tightly regulated by a complex network of proteins and signaling pathways, ensuring that each daughter cell receives the correct amount of cytoplasm and organelles.
Overall, cytokinesis is a crucial step in the cell cycle, ensuring that genetic material is equally distributed between daughter cells and allowing for the growth and development of multicellular organisms.
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This question is part of the following fields:
- Genetics
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Question 92
Incorrect
-
Which statement about XYY syndrome is correct?
Your Answer:
Correct Answer: Affected individuals are usually asymptomatic
Explanation:XYY Syndrome
XYY Syndrome, also known as Jacobs’ Syndrome of super-males, is a genetic condition where males have an extra Y chromosome, resulting in a 47, XYY karyotype. In some cases, mosaicism may occur, resulting in a 47,XYY/46,XY karyotype. The error leading to the 47,XYY genotype occurs during spermatogenesis of post-zygotic mitosis. The prevalence of XYY Syndrome is as high as 1:1000 male live births, but many cases go unidentified as they are not necessarily associated with physical of cognitive impairments. The most common features are high stature and a strong build, and fertility and sexual development are usually unaffected. In the past, XYY Syndrome was linked to aggressiveness and deviance, but this is likely due to intermediate factors such as reduced IQ and social deprivation. XYY Syndrome is best thought of as a risk factor rather than a cause. There is an increased risk of developmental disorders such as learning difficulties, ASD, ADHD, and emotional problems.
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This question is part of the following fields:
- Genetics
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Question 93
Incorrect
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What is the rate of schizophrenia concordance among dizygotic twins?
Your Answer:
Correct Answer: 17%
Explanation:The rate of concordance for schizophrenia in DZ twins is 17%.
Schizophrenia: A Genetic Disorder
Adoption studies have consistently shown that biological relatives of patients with schizophrenia have an increased risk of developing the disorder. Schizophrenia is a complex disorder with incomplete penetrance, as evidenced by the fact that monozygotic twins have a concordance rate of approximately 50%, while dizygotic twins have a concordance rate of 17%. This indicates a significant genetic contribution to the disorder, with an estimated heritability of 80%. Segregation analysis suggests that schizophrenia follows a multifactorial model.
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This question is part of the following fields:
- Genetics
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Question 94
Incorrect
-
What is the primary role of the proteasome?
Your Answer:
Correct Answer: To degrade cellular proteins
Explanation:Nissl substance is composed of rough endoplasmic reticulum with free ribosomes and is responsible for synthesizing proteins. The Golgi apparatus modifies, organizes, and packages macromolecules for either secretion of internal use. Mitochondria are involved in producing energy for the cell. Microfilaments and microtubules provide structural support and aid in transportation within the cell. Lysosomes are spherical structures that contain digestive enzymes, which break down cellular waste and protect against threats such as viruses.
The Function of Proteasomes in Protein Degradation
Proteasomes play a crucial role in breaking down proteins that are produced within the cell. These cylindrical complexes are present in both the nucleus and cytoplasm of the cell. The process of protein degradation involves the tagging of proteins with a small protein called ubiquitin. The proteasome consists of a core structure made up of four stacked rings surrounding a central pore. Each ring is composed of seven individual proteins. This structure allows for the efficient degradation of proteins, ensuring that the cell can maintain proper protein levels and function.
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This question is part of the following fields:
- Genetics
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Question 95
Incorrect
-
Which of the following is associated with dynamic mutations?
Your Answer:
Correct Answer: Fragile X
Explanation:Trinucleotide Repeat Disorders: Understanding the Genetic Basis
Trinucleotide repeat disorders are genetic conditions that arise due to the abnormal presence of an expanded sequence of trinucleotide repeats. These disorders are characterized by the phenomenon of anticipation, which refers to the amplification of the number of repeats over successive generations. This leads to an earlier onset and often a more severe form of the disease.
The table below lists the trinucleotide repeat disorders and the specific repeat sequences involved in each condition:
Condition Repeat Sequence Involved
Fragile X Syndrome CGG
Myotonic Dystrophy CTG
Huntington’s Disease CAG
Friedreich’s Ataxia GAA
Spinocerebellar Ataxia CAGThe mutations responsible for trinucleotide repeat disorders are referred to as ‘dynamic’ mutations. This is because the number of repeats can change over time, leading to a range of clinical presentations. Understanding the genetic basis of these disorders is crucial for accurate diagnosis, genetic counseling, and the development of effective treatments.
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This question is part of the following fields:
- Genetics
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Question 96
Incorrect
-
Which base pairs are found within DNA?
Your Answer:
Correct Answer: Guanine and cytosine
Explanation:Genomics: Understanding DNA, RNA, Transcription, and Translation
Deoxyribonucleic acid (DNA) is a molecule composed of two chains that coil around each other to form a double helix. DNA is organised into chromosomes, and each chromosome is made up of DNA coiled around proteins called histones. RNA, on the other hand, is made from a long chain of nucleotide units and is usually single-stranded. RNA is transcribed from DNA by enzymes called RNA polymerases and is central to protein synthesis.
Transcription is the synthesis of RNA from a DNA template, and it consists of three main steps: initiation, elongation, and termination. RNA polymerase binds at a sequence of DNA called the promoter, and the transcriptome is the collection of RNA molecules that results from transcription. Translation, on the other hand, refers to the synthesis of polypeptides (proteins) from mRNA. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.
The process of translation involves messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transfer RNAs, of tRNAs, connect mRNA codons to the amino acids they encode, while ribosomes are the structures where polypeptides (proteins) are built. Like transcription, translation also consists of three stages: initiation, elongation, and termination. In initiation, the ribosome assembles around the mRNA to be read and the first tRNA carrying the amino acid methionine. In elongation, the amino acid chain gets longer, and in termination, the finished polypeptide chain is released.
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This question is part of the following fields:
- Genetics
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Question 97
Incorrect
-
What is the more commonly used name for Trisomy 13 syndrome?
Your Answer:
Correct Answer: Patau syndrome
Explanation:Genetic Conditions and Their Features
Genetic conditions are disorders caused by abnormalities in an individual’s DNA. These conditions can affect various aspects of a person’s health, including physical and intellectual development. Some of the most common genetic conditions and their features are:
– Downs (trisomy 21): Short stature, almond-shaped eyes, low muscle tone, and intellectual disability.
– Angelman syndrome (Happy puppet syndrome): Flapping hand movements, ataxia, severe learning disability, seizures, and sleep problems.
– Prader-Willi: Hyperphagia, excessive weight gain, short stature, and mild learning disability.
– Cri du chat: Characteristic cry, hypotonia, down-turned mouth, and microcephaly.
– Velocardiofacial syndrome (DiGeorge syndrome): Cleft palate, cardiac problems, and learning disabilities.
– Edwards syndrome (trisomy 18): Severe intellectual disability, kidney malformations, and physical abnormalities.
– Lesch-Nyhan syndrome: Self-mutilation, dystonia, and writhing movements.
– Smith-Magenis syndrome: Pronounced self-injurious behavior, self-hugging, and a hoarse voice.
– Fragile X: Elongated face, large ears, hand flapping, and shyness.
– Wolf Hirschhorn syndrome: Mild to severe intellectual disability, seizures, and physical abnormalities.
– Patau syndrome (trisomy 13): Severe intellectual disability, congenital heart malformations, and physical abnormalities.
– Rett syndrome: Regression and loss of skills, hand-wringing movements, and profound learning disability.
– Tuberous sclerosis: Hamartomatous tumors, epilepsy, and behavioral issues.
– Williams syndrome: Elfin-like features, social disinhibition, and advanced verbal skills.
– Rubinstein-Taybi syndrome: Short stature, friendly disposition, and moderate learning disability.
– Klinefelter syndrome: Extra X chromosome, low testosterone, and speech and language issues.
– Jakob’s syndrome: Extra Y chromosome, tall stature, and lower mean intelligence.
– Coffin-Lowry syndrome: Short stature, slanting eyes, and severe learning difficulty.
– Turner syndrome: Short stature, webbed neck, and absent periods.
– Niemann Pick disease (types A and B): Abdominal swelling, cherry red spot, and feeding difficulties.It is important to note that these features may vary widely among individuals with the same genetic condition. Early diagnosis and intervention can help individuals with genetic conditions reach their full potential and improve their quality of life.
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This question is part of the following fields:
- Genetics
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Question 98
Incorrect
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What is one assumption of the Hardy-Weinberg equilibrium?
Your Answer:
Correct Answer: Mating between individuals is random
Explanation:Hardy-Weinberg Principle and Allele Frequency
Allele frequency refers to the proportion of a population that carries a specific variant at a particular gene locus. It can be calculated by dividing the number of individual alleles of a certain type by the total number of alleles in a population. The Hardy-Weinberg Principle states that both allele and genotype frequencies in a population remain constant from generation to generation unless specific disturbing influences are introduced. To remain in equilibrium, five conditions must be met, including no mutations, no gene flow, random mating, a sufficiently large population, and no natural selection. The Hardy-Weinberg Equation is used to predict the frequency of alleles in a population, and it can be used to estimate the carrier frequency of genetic diseases. For example, if the incidence of PKU is one in 10,000 babies, then the carrier frequency in the general population is 1/50. Couples with a previous child with PKU have a 25% chance of having another affected child.
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This question is part of the following fields:
- Genetics
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Question 99
Incorrect
-
Which statement is false regarding autosomal dominant conditions?
Your Answer:
Correct Answer: Show horizontal transmission
Explanation:X-linked transmission is characterized by a Knight’s move pattern.
Modes of Inheritance
Genetic disorders can be passed down from one generation to the next in various ways. There are four main modes of inheritance: autosomal dominant, autosomal recessive, X-linked (sex-linked), and multifactorial.
Autosomal Dominant Inheritance
Autosomal dominant inheritance occurs when one faulty gene causes a problem despite the presence of a normal one. This type of inheritance shows vertical transmission, meaning it is based on the appearance of the family pedigree. If only one parent is affected, there is a 50% chance of each child expressing the condition. Autosomal dominant conditions often show pleiotropy, where a single gene influences several characteristics.
Autosomal Recessive Inheritance
In autosomal recessive conditions, a person requires two faulty copies of a gene to manifest a disease. A person with one healthy and one faulty gene will generally not manifest a disease and is labelled a carrier. Autosomal recessive conditions demonstrate horizontal transmission.
X-linked (Sex-linked) Inheritance
In X-linked conditions, the problem gene lies on the X chromosome. This means that all males are affected. Like autosomal conditions, they can be dominant of recessive. Affected males are unable to pass the condition on to their sons. In X-linked recessive conditions, the inheritance pattern is characterised by transmission from affected males to male grandchildren via affected carrier daughters.
Multifactorial Inheritance
Multifactorial conditions result from the interaction between genes from both parents and the environment.
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This question is part of the following fields:
- Genetics
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Question 100
Incorrect
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A 16 year old boy is brought to clinic by his parents who are worried about his recent behavior of talking to imaginary people and exhibiting unusual behavior. Upon further inquiry, it is discovered that he has a history of learning disability and was born with a cleft palate and a heart defect. The parents also report that he has had frequent bouts of pneumonia. Based on this information, what is the most likely diagnosis?
Your Answer:
Correct Answer: DiGeorge syndrome
Explanation:DiGeorge syndrome is primarily caused by a deletion on chromosome 22 and presents with a range of symptoms. To aid in remembering the chromosome involved and some of the signs and symptoms, a mnemonic is used. These include cardiac abnormalities such as tetralogy of Fallot, abnormal facies with almond-shaped eyes and low-set ears, thymic aplasia leading to recurrent infections, cleft palate, and hypocalcemia/hypoparathyroidism causing short stature and seizures. Additionally, individuals with DiGeorge syndrome often have a degree of learning disability and are at an increased risk for psychiatric conditions such as depression, ADHD, and schizophrenia.
Genetic Conditions and Their Features
Genetic conditions are disorders caused by abnormalities in an individual’s DNA. These conditions can affect various aspects of a person’s health, including physical and intellectual development. Some of the most common genetic conditions and their features are:
– Downs (trisomy 21): Short stature, almond-shaped eyes, low muscle tone, and intellectual disability.
– Angelman syndrome (Happy puppet syndrome): Flapping hand movements, ataxia, severe learning disability, seizures, and sleep problems.
– Prader-Willi: Hyperphagia, excessive weight gain, short stature, and mild learning disability.
– Cri du chat: Characteristic cry, hypotonia, down-turned mouth, and microcephaly.
– Velocardiofacial syndrome (DiGeorge syndrome): Cleft palate, cardiac problems, and learning disabilities.
– Edwards syndrome (trisomy 18): Severe intellectual disability, kidney malformations, and physical abnormalities.
– Lesch-Nyhan syndrome: Self-mutilation, dystonia, and writhing movements.
– Smith-Magenis syndrome: Pronounced self-injurious behavior, self-hugging, and a hoarse voice.
– Fragile X: Elongated face, large ears, hand flapping, and shyness.
– Wolf Hirschhorn syndrome: Mild to severe intellectual disability, seizures, and physical abnormalities.
– Patau syndrome (trisomy 13): Severe intellectual disability, congenital heart malformations, and physical abnormalities.
– Rett syndrome: Regression and loss of skills, hand-wringing movements, and profound learning disability.
– Tuberous sclerosis: Hamartomatous tumors, epilepsy, and behavioral issues.
– Williams syndrome: Elfin-like features, social disinhibition, and advanced verbal skills.
– Rubinstein-Taybi syndrome: Short stature, friendly disposition, and moderate learning disability.
– Klinefelter syndrome: Extra X chromosome, low testosterone, and speech and language issues.
– Jakob’s syndrome: Extra Y chromosome, tall stature, and lower mean intelligence.
– Coffin-Lowry syndrome: Short stature, slanting eyes, and severe learning difficulty.
– Turner syndrome: Short stature, webbed neck, and absent periods.
– Niemann Pick disease (types A and B): Abdominal swelling, cherry red spot, and feeding difficulties.It is important to note that these features may vary widely among individuals with the same genetic condition. Early diagnosis and intervention can help individuals with genetic conditions reach their full potential and improve their quality of life.
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This question is part of the following fields:
- Genetics
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Question 101
Incorrect
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What is the definition of genomic imprinting?
Your Answer:
Correct Answer: The observation that portions of DNA behave differently depending on whether they are inherited from the mother of father
Explanation:Genomic Imprinting and its Role in Psychiatric Disorders
Genomic imprinting is a phenomenon where a piece of DNA behaves differently depending on whether it is inherited from the mother of the father. This is because DNA sequences are marked of imprinted in the ovaries and testes, which affects their expression. In psychiatry, two classic examples of genomic imprinting disorders are Prader-Willi and Angelman syndrome.
Prader-Willi syndrome is caused by a deletion of chromosome 15q when inherited from the father. This disorder is characterized by hypotonia, short stature, polyphagia, obesity, small gonads, and mild mental retardation. On the other hand, Angelman syndrome, also known as Happy Puppet syndrome, is caused by a deletion of 15q when inherited from the mother. This disorder is characterized by an unusually happy demeanor, developmental delay, seizures, sleep disturbance, and jerky hand movements.
Overall, genomic imprinting plays a crucial role in the development of psychiatric disorders. Understanding the mechanisms behind genomic imprinting can help in the diagnosis and treatment of these disorders.
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This question is part of the following fields:
- Genetics
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Question 102
Incorrect
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You are requested to conduct a home visit for a 35-year-old male patient who is experiencing depression. He also complains of poor coordination and you observe that he has an unsteady gait. During the consultation, you learn that his father passed away at the age of 55 due to a degenerative disease and had exhibited abnormal jerky movements for a few years. Based on this information, which of the following trinucleotide repeat disorders would you suspect the most?
Your Answer:
Correct Answer: CAG
Explanation:The historical evidence indicates that the individual may be affected by Huntington’s disease, which is a genetic disorder caused by the expansion of a trinucleotide repeat in the huntingtin gene.
Trinucleotide Repeat Disorders: Understanding the Genetic Basis
Trinucleotide repeat disorders are genetic conditions that arise due to the abnormal presence of an expanded sequence of trinucleotide repeats. These disorders are characterized by the phenomenon of anticipation, which refers to the amplification of the number of repeats over successive generations. This leads to an earlier onset and often a more severe form of the disease.
The table below lists the trinucleotide repeat disorders and the specific repeat sequences involved in each condition:
Condition Repeat Sequence Involved
Fragile X Syndrome CGG
Myotonic Dystrophy CTG
Huntington’s Disease CAG
Friedreich’s Ataxia GAA
Spinocerebellar Ataxia CAGThe mutations responsible for trinucleotide repeat disorders are referred to as ‘dynamic’ mutations. This is because the number of repeats can change over time, leading to a range of clinical presentations. Understanding the genetic basis of these disorders is crucial for accurate diagnosis, genetic counseling, and the development of effective treatments.
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This question is part of the following fields:
- Genetics
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Question 103
Incorrect
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What is the effect of being heterozygous for the APOE4 allele on the risk of Alzheimer's compared to those who do not have the allele?
Your Answer:
Correct Answer: Increases it by a factor of 3
Explanation:Genetics plays a role in the development of Alzheimer’s disease, with different genes being associated with early onset and late onset cases. Early onset Alzheimer’s, which is rare, is linked to three genes: amyloid precursor protein (APP), presenilin one (PSEN-1), and presenilin two (PSEN-2). The APP gene, located on chromosome 21, produces a protein that is a precursor to amyloid. The presenilins are enzymes that cleave APP to produce amyloid beta fragments, and alterations in the ratios of these fragments can lead to plaque formation. Late onset Alzheimer’s is associated with the apolipoprotein E (APOE) gene on chromosome 19, with the E4 variant increasing the risk of developing the disease. People with Down’s syndrome are also at high risk of developing Alzheimer’s due to inheriting an extra copy of the APP gene.
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This question is part of the following fields:
- Genetics
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Question 104
Incorrect
-
What is the term used to describe the process of translating a segment of genetic information from DNA to RNA?
Your Answer:
Correct Answer: Transcription
Explanation:Genomics: Understanding DNA, RNA, Transcription, and Translation
Deoxyribonucleic acid (DNA) is a molecule composed of two chains that coil around each other to form a double helix. DNA is organised into chromosomes, and each chromosome is made up of DNA coiled around proteins called histones. RNA, on the other hand, is made from a long chain of nucleotide units and is usually single-stranded. RNA is transcribed from DNA by enzymes called RNA polymerases and is central to protein synthesis.
Transcription is the synthesis of RNA from a DNA template, and it consists of three main steps: initiation, elongation, and termination. RNA polymerase binds at a sequence of DNA called the promoter, and the transcriptome is the collection of RNA molecules that results from transcription. Translation, on the other hand, refers to the synthesis of polypeptides (proteins) from mRNA. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.
The process of translation involves messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transfer RNAs, of tRNAs, connect mRNA codons to the amino acids they encode, while ribosomes are the structures where polypeptides (proteins) are built. Like transcription, translation also consists of three stages: initiation, elongation, and termination. In initiation, the ribosome assembles around the mRNA to be read and the first tRNA carrying the amino acid methionine. In elongation, the amino acid chain gets longer, and in termination, the finished polypeptide chain is released.
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This question is part of the following fields:
- Genetics
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Question 105
Incorrect
-
Which statement about the genetic epidemiology of schizophrenia is accurate?
Your Answer:
Correct Answer: Adoption studies consistently show an increased risk of schizophrenia in the biological relatives of patients with schizophrenia
Explanation:Schizophrenia: A Genetic Disorder
Adoption studies have consistently shown that biological relatives of patients with schizophrenia have an increased risk of developing the disorder. Schizophrenia is a complex disorder with incomplete penetrance, as evidenced by the fact that monozygotic twins have a concordance rate of approximately 50%, while dizygotic twins have a concordance rate of 17%. This indicates a significant genetic contribution to the disorder, with an estimated heritability of 80%. Segregation analysis suggests that schizophrenia follows a multifactorial model.
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This question is part of the following fields:
- Genetics
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Question 106
Incorrect
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What is the cause of the formation of the 'Barr body'?
Your Answer:
Correct Answer: Lyonization
Explanation:Lyonization: The Process of X-Inactivation
The X chromosome is crucial for proper development and cell viability, containing over 1,000 essential genes. However, females carry two copies of the X chromosome, which can result in a potentially toxic double dose of X-linked genes. To address this imbalance, females undergo a process called Lyonization, of X-inactivation, where one of their two X chromosomes is transcriptionally silenced. The silenced X chromosome then condenses into a compact structure known as a Barr body, which remains in a silent state.
X-inactivation occurs randomly, with no preference for the paternal or maternal X chromosome. It takes place early in embryogenesis, soon after fertilization when the dividing conceptus is about 16-32 cells big. This process occurs in all somatic cells of women, but not in germ cells involved in forming gametes. X-inactivation affects most, but not all, genes on the X chromosome. If a cell has more than two X chromosomes, the extra Xs are also inactivated.
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This question is part of the following fields:
- Genetics
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Question 107
Incorrect
-
A mutation affecting the transcriptional activity of a new gene associated with Alzheimer's disease is reported. The mutation is most likely to be in which of the following?
Your Answer:
Correct Answer: Promoter region
Explanation:Genomics: Understanding DNA, RNA, Transcription, and Translation
Deoxyribonucleic acid (DNA) is a molecule composed of two chains that coil around each other to form a double helix. DNA is organised into chromosomes, and each chromosome is made up of DNA coiled around proteins called histones. RNA, on the other hand, is made from a long chain of nucleotide units and is usually single-stranded. RNA is transcribed from DNA by enzymes called RNA polymerases and is central to protein synthesis.
Transcription is the synthesis of RNA from a DNA template, and it consists of three main steps: initiation, elongation, and termination. RNA polymerase binds at a sequence of DNA called the promoter, and the transcriptome is the collection of RNA molecules that results from transcription. Translation, on the other hand, refers to the synthesis of polypeptides (proteins) from mRNA. Translation takes place on ribosomes in the cell cytoplasm, where mRNA is read and translated into the string of amino acid chains that make up the synthesized protein.
The process of translation involves messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transfer RNAs, of tRNAs, connect mRNA codons to the amino acids they encode, while ribosomes are the structures where polypeptides (proteins) are built. Like transcription, translation also consists of three stages: initiation, elongation, and termination. In initiation, the ribosome assembles around the mRNA to be read and the first tRNA carrying the amino acid methionine. In elongation, the amino acid chain gets longer, and in termination, the finished polypeptide chain is released.
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This question is part of the following fields:
- Genetics
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Question 108
Incorrect
-
What is a true statement about Williams syndrome?
Your Answer:
Correct Answer: It is commonly associated with hyperacusis
Explanation:Williams syndrome is a genetic condition resulting from the deletion of a portion of chromosome 7. Individuals with this syndrome often experience cognitive challenges, but possess strong social skills and impressive language abilities. While hyperacusis is a common symptom, those affected often have a passion for music and may excel in this area. Williams syndrome is also linked to endocrine irregularities, specifically hypercalcemia.
Understanding Williams Syndrome
Williams syndrome is a rare neurodevelopmental disorder that is characterized by distinct physical and behavioral traits. Individuals with this syndrome have a unique facial appearance, including a low nasal bridge and a cheerful demeanor. They also tend to have mild to moderate mental retardation and are highly sociable and verbal.
Children with Williams syndrome are particularly sensitive to sound and may overreact to loud of high-pitched noises. The syndrome is caused by a deletion in the q11.23 region of chromosome 7, which codes for more than 20 genes. This deletion typically occurs during the recombination phase of meiosis and can be detected using fluorescent in situ hybridization (FISH).
Although Williams syndrome is an autosomal dominant condition, most cases are not inherited and occur sporadically in individuals with no family history of the disorder. With a prevalence of around 1 in 20,000, Williams syndrome is a rare condition that requires specialized care and support.
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This question is part of the following fields:
- Genetics
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Question 109
Incorrect
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Which of the following is not a trinucleotide repeat disorder?
Your Answer:
Correct Answer: Williams syndrome
Explanation:Deletion of genetic material on chromosome 7 is the underlying cause of William’s syndrome.
Trinucleotide Repeat Disorders: Understanding the Genetic Basis
Trinucleotide repeat disorders are genetic conditions that arise due to the abnormal presence of an expanded sequence of trinucleotide repeats. These disorders are characterized by the phenomenon of anticipation, which refers to the amplification of the number of repeats over successive generations. This leads to an earlier onset and often a more severe form of the disease.
The table below lists the trinucleotide repeat disorders and the specific repeat sequences involved in each condition:
Condition Repeat Sequence Involved
Fragile X Syndrome CGG
Myotonic Dystrophy CTG
Huntington’s Disease CAG
Friedreich’s Ataxia GAA
Spinocerebellar Ataxia CAGThe mutations responsible for trinucleotide repeat disorders are referred to as ‘dynamic’ mutations. This is because the number of repeats can change over time, leading to a range of clinical presentations. Understanding the genetic basis of these disorders is crucial for accurate diagnosis, genetic counseling, and the development of effective treatments.
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This question is part of the following fields:
- Genetics
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Question 110
Incorrect
-
Which gene is believed to have the most significant influence on the likelihood of developing alcohol addiction?
Your Answer:
Correct Answer: ADH1B
Explanation:Genetics and Alcoholism
Alcoholism tends to run in families, and several studies confirm that biological children of alcoholics are more likely to develop alcoholism even when adopted by parents without the condition. Monozygotic twins have a greater concordance rate for alcoholism than dizygotic twins. Heritability estimates range from 45 to 65 percent for both men and women. While genetic differences affect risk, there is no “gene for alcoholism,” and both environmental and social factors weigh heavily on the outcome.
The genes with the clearest contribution to the risk for alcoholism and alcohol consumption are alcohol dehydrogenase 1B (ADH1B) and aldehyde dehydrogenase 2 (ALDH2). The first step in ethanol metabolism is oxidation to acetaldehyde, by ADHs. The second step is metabolism of the acetaldehyde to acetate by ALDHs. Individuals carrying even a single copy of the ALDH2*504K display the “Asian flushing reaction” when they consume even small amounts of alcohol. There is one significant genetic polymorphism of the ALDH2 gene, resulting in allelic variants ALDH2*1 and ALDH2*2, which is virtually inactive. ALDH2*2 is present in about 50 percent of the Taiwanese, Han Chinese, and Japanese populations. It is extremely rare outside Asia. Nearly no individuals of European of African descent carry this allele. ALDH2*504K has repeatedly been demonstrated to have a protective effect against alcohol use disorders.
The three different class I gene loci, ADH1A (alpha), ADH1B (beta), and ADH1C (gamma) are situated close to each other in the region 4q2123. The alleles ADH1C*1 and ADH1B*2 code for fast metabolism of alcohol. The ADH1B*1 slow allele is very common among Caucasians, with approximately 95 percent having the homozygous ADH1B*1/1 genotype and 5 percent having the heterozygous ADH1B*1/2 genotype. The ADH1B*2 allele is the most common allele in Asian populations. In African populations, the ADH1B*1 allele is the most common.
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This question is part of the following fields:
- Genetics
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Question 111
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