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Question 1
Incorrect
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Which of the following is the leading cause of Down Syndrome?
Your Answer: Mitotic Nondisjunction after conception
Correct Answer: Nondisjunction maternal gamete
Explanation:Most of the cases of down syndrome occur due to non disjunction trisomy 21 which is associated with increased maternal age. The non disjunction occurs in the maternal gametes.
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This question is part of the following fields:
- Genetics
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Question 2
Incorrect
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A pregnant patient who is needle phobic has her nuchal translucency (NT) scan but refuses serum markers. You advise her the False Positive Rate of the scan is 5%. What would you advise the mother regarding the detection rate of Down Syndrome using NT alone?
Your Answer: 40%
Correct Answer: 70%
Explanation:The nuchal lucency measurement is the measure of the nuchal pad thickness. Children with down syndrome have an increased thickness of the nuchal pad. The risk of down’s syndrome increases with maternal age. The nuchal lucency test has an accuracy rate of 70%.
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This question is part of the following fields:
- Genetics
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Question 3
Incorrect
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Regarding Turner syndrome which of the following statements is true?
Your Answer: Complete monosomy is rare accounting for <10% of cases of Turners
Correct Answer: Only 1% of affected foetuses will survive to term
Explanation:The incidence of 45,XO turner syndrome is around 1 in 8000 live births. Approximately 1% of monosomy X female embryos survive. Phenotypically they are females and 90% do not develop secondary sexual characteristics and hormone replacement is required.
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This question is part of the following fields:
- Genetics
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Question 4
Correct
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Regarding twin pregnancies all of the following are correct EXCEPT:
Your Answer: Identical or monozygotic twins arise from fertilization of two ovum
Explanation:Monozygotic (MZ) twins originate when a single egg is fertilized to form one zygote, which then divides into two embryos. Although they share the same genotype they are not phenotypically identical.
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This question is part of the following fields:
- Genetics
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Question 5
Correct
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You see a patient in fertility clinic who you suspect has Klinefelters. What is the likely karyotype?
Your Answer: 47XXY
Explanation:Klinefelter syndrome occurs in 1:1000 individuals. They are phenotypically male and genotypically they have 47,XXY chromosomes. These individuals have small testes, are tall with disproportionate long lower limbs.40% will also have gynecomastia.
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This question is part of the following fields:
- Genetics
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Question 6
Incorrect
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A 40 year old women who is 13 weeks pregnant is found to have be high risk for Downs following the combined screening test. What is the most appropriate further test to see if the foetus is affected?
Your Answer: Amniocentesis
Correct Answer: Chorionic Villous Sampling
Explanation:Chorion villus sampling is an invasive procedure which aims to collect the rapidly dividing cells in the placenta. It is used for numerous reasons including detection of early pregnancy, viability of the foetus, singleton pregnancy, confirm gestation age and for prenatal diagnosis of the fetal chromosomal abnormalities including diagnosis of Down’s syndrome. However it hold a 2% chance of miscarriage during the procedure. Nuchal thickness and imaging are part of the combined test that must have been performed before.
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This question is part of the following fields:
- Genetics
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Question 7
Correct
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All are true about monozygotic pregnancy, EXCEPT:
Your Answer: The 1st commonly presents as breech
Explanation:The 1st commonly presents as cephalic. Monozygotic (MZ) twins originate when a single egg is fertilized to form one zygote, which then divides into two embryos. Although they share the same genotype they are not phenotypically identical.
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This question is part of the following fields:
- Genetics
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Question 8
Correct
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You are called to assist in an initially midwife led delivery. Upon delivering a female baby you notice the baby has partial fusion of the labioscrotal folds. You suspect congenital adrenal hyperplasia. Which of the following is the most common enzyme deficiency?
Your Answer: 21-hydroxylase
Explanation:Congenital Adrenal Hyperplasia leads to the virilization of the foetus. It occurs due to an enzyme deficiency in the corticosteroid production pathway i.e. 21-hydroxylase which converts progesterone to deoxycorticosterone. The reduced levels of corticosteroids results in the negative feedback loop that leads to adrenal hyperplasia.
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This question is part of the following fields:
- Genetics
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Question 9
Correct
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Question 10
Correct
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Regarding monozygotic twins, all of the following are correct, EXCEPT:
Your Answer: Has a constant incidence 1:600 births
Explanation:The incidence of monozygotic twins is constant worldwide (approximately 4 per 1000 births). Approximately two thirds of twins are dizygotic.
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This question is part of the following fields:
- Genetics
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