A man has a condition where all of his gametes undergo nondi

A man has a condition where all of his gametes undergo nondisjunction of the sex chromosomes in meiosis I, but meiosis II proceeds normally. He mates with a woman who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Klinefelter syndrome (XXY)? Assume that all gametes and zygotes are viable.

1/8

1/4

1/3

1/2

0

Solution

Answer: 1/2

Nondisjunction occurs when homologous chromosomes, in this case the X and Y or two X sex chromosomes, fail to separate, producing a sperm with an X and a Y chromosome. If the man has nondisjunction of all of his sperms (at meiosis1), then 50% or ½ of the sperms are XY.

Therefore  probability of child with Klinefelter syndrome (XXY) will be 1/2

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