Two forms of hemophilia are determined by genes on the X chromosome in humans.Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man.What is the probability that their first son will have hemophilia?
A)zero
B)1/2
C)100%
D)1/4
E)1/3

Question

Quizplus · Accepted Answer

Since hemophilia is X-linked and the woman's father had hemophilia, she must carry one allele for hemophilia (being heterozygous XhX). The normal man can only contribute a Y chromosome to a son, making the son's genotype dependent on which X chromosome he inherits from his mother. There's a 50% chance he will inherit the X chromosome carrying the hemophilia allele (XhY), leading to hemophilia.

Two Forms of Hemophilia Are Determined by Genes on the X