A woman has a condition where all of her gametes undergo nondisjunction of chromosome 21 in meiosis I, but meiosis II proceeds normally. She mates with a man who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Down syndrome? Assume that all gametes and zygotes are viable.
A) 1/8
B) 1/4
C) 1/3
D) 1/2
E) 0

Question

Quizplus · Accepted Answer

Since all of the woman's gametes have two copies of chromosome 21 due to nondisjunction in meiosis I, and the man's gametes are normal with one copy, each fertilized egg will have three copies of chromosome 21, resulting in Down syndrome. Thus, the probability is 1/2.

A Woman Has a Condition Where All of Her Gametes