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Question 1
Incorrect
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Regarding monozygotic twins, all of the following are correct, EXCEPT:
Your Answer: Has a constant incidence of 1:250 births
Correct 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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Question 2
Incorrect
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A woman has undergone genetic testing due to her family history and has the BRCA 1 gene. What would you advise her lifetime risk of ovarian cancer is?
Your Answer: 70%
Correct Answer: 40%
Explanation:The most common hereditary cancer in the breast ovarian cancer syndrome accounts for 90% of the hereditary cancers. It is due to mutations in the BRCA 1 and BRCA 2 genes, most commonly the BRCA 1 gene accounting for 70% life time risk of breast cancer and 40% life time risk of ovarian cancer.
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This question is part of the following fields:
- Genetics
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Question 3
Correct
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Regarding Turner syndrome which of the following statements is true?
Your 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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Which of the following is the leading cause of Down Syndrome?
Your 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 5
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 genes is most likely to be mutated?
Your Answer: CYP21A
Explanation:CAH leads to virilization of the female foetus. It occurs to an enzyme deficiency (21-hydroxylase). This results in a reduced levels of corticosteroids from being circulated resulting in hyperplasia of the adrenal glands and increased progesterone production. The CYP21A gene has been implicated in causes this deficiency.
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This question is part of the following fields:
- Genetics
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Question 6
Correct
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A women has undergone genetic testing due to her family history and has the BRCA 2 gene. What would you advise her lifetime risk of breast cancer is?
Your Answer: 45%
Explanation:The life time risk of breast cancer in BRCA 2 gene is 45% and of ovarian cancer is 15%.
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This question is part of the following fields:
- Genetics
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Question 7
Correct
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Which of the following statements regarding BRCA gene mutations is true?
Your Answer: They account for around 25% of inherited breast cancers
Explanation:Hereditary breast cancers account for 10 % of the cases. BRCA gene mutations account for 25 % of these cancers.
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This question is part of the following fields:
- Genetics
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Question 8
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 9
Correct
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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: 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 10
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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