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 daughter will have hemophilia?
A)1/3
B)zero
C)1/4
D)1/2
E)100%

Question

Quizplus · Accepted Answer

Since the woman is phenotypically normal, she must have inherited one normal X chromosome from her mother and one affected X chromosome from her father who had hemophilia. Therefore, she is a carrier of hemophilia. When she has a child, there is a 50% chance that she will pass on her normal X chromosome and a 50% chance that she will pass on her affected X chromosome. However, since the father is normal and only has one X chromosome to pass on, he can only pass on a normal X chromosome. Therefore, the probability of their daughter having hemophilia is zero.

Two Forms of Hemophilia Are Determined by Genes on the X