Suppose That a Man and Woman Have a Son with a Rare

Multiple Choice

Suppose that a man and woman have a son with a rare genetic disorder known to be X-linked. There is no occurrence of the disorder on the woman's side of the family, but the man's brother has it, as does her father. What is the probability that the son's defective allele came from the man?

A) 0%
B) 25%
C) 50%
D) 100%