Essential Genetics 6th Edition by Daniel Hartl

Exercise 7

A recessive mutation of an X-linked gene in humans results in hemophilia, a condition marked by a prolonged increase in the time needed for blood clotting. Suppose that a mating between phenotypically normal parents produces two normal daughters and one son affected with hemophilia.
(a) What is the probability that at least one of the daughters is a heterozygous carrier?
(b) If one of the daughters and a normal male produce a son, what is the probability that the son will be affected?