Practice MCAT Question - Q158 - Answer!
A hemophiliac woman and her husband whose blood clots normally, have a son. What is the probability that this child will have hemophilia? Hemophilia is a sex-linked recessive trait.
A. 25%
B. 50%
C. 75%
D. 100%
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The correct answer is (D). If mom has hemophilia, her genotype is XhXh. She can only contribute an X chromosome with the recessive allele for hemophilia to all her sons. (They must receive the Y chromosome from dad in order to be sons in the first place!) Therefore, all sons produced by this couple will have the genotype XhY, and will have hemophilia.
