TBR Bio Book I page 113 #12 "What is the probability that a woman whose father has hemophilia and who marries a normal man will have an affected son" Answer: 50% My answer: 25% Hemophilia is sex-linked recessive. I get that to have an affected son, the woman (who is a carrier) must pass her affected X chromosome to the boy. There is a 50% chance of this. But what about GENDER? Why don't you account for gender? If you draw out the punnet square, you will see that only one box (25% chance) is for an affected son.