USMLE Step 1 Question of the Day
Quiz-summary
0 of 1 questions completed
Questions:
- 1
Information
USMLE Step 1 Questions
You have already completed the quiz before. Hence you can not start it again.
Quiz is loading...
You must sign in or sign up to start the quiz.
You have to finish following quiz, to start this quiz:
Results
Time has elapsed
You have reached 0 of 0 points, (0)
Categories
- Genetics 0%
-
Question:
A couple that is trying to conceive a child once gave birth to a baby that died at 7 months of age. This previous baby was born with severely diminished motor tone and tongue fasciculations. Autopsy revealed massive degeneration of the baby’s anterior horns, which was attributed to Werdnig-Hoffman Disease. What is the probability that another child conceived by this couple will have the same disease?
Correct Answer: B. 25%
Werdnig-Hoffman disease is inherited autosomal recessively. Since each parent is carrying one recessive allele (since one baby has already had the disease), all future children have 25% chance of being recessive homozygous for gene (B).
Werdnig-Hoffman disease is fatal at a very young age, and so is not a negative dominant trait (or the parents would have died), so 100% (E) is incorrect.
For straight-forward autosomal inheritance patterns, you could also eliminate (A) 10%, as no combination of dominant/recessive alleles (based on a Punnett-square analysis) would result in this probability.
Autosomal dominant traits are inherited at a 75% rate (D), while the heterozygous genotype is inherited at a 50% rate (C).
- 1
- Answered
- Review
-
Question 1 of 1
1. Question
Category: GeneticsA couple that is trying to conceive a child once gave birth to a baby that died at 7 months of age. This previous baby was born with severely diminished motor tone and tongue fasciculations. Autopsy revealed massive degeneration of the baby’s anterior horns, which was attributed to Werdnig-Hoffman Disease. What is the probability that another child conceived by this couple will have the same disease?
Correct
Incorrect