James is a 42-year-old man with hemophilia, a sex-linked recessive condition. His daughter, Susan, who has normal blood clotting, is married to Fred who also has hemophilia. Susan and Fred are expecting their first child and an ultrasound shows that the fetus is male. What is the approximate probability that their new son will have hemophilia?

Question

Quizplus · Accepted Answer

Susan is a carrier of hemophilia (X^HX^h) since her father has hemophilia (X^hY) and she has normal clotting. Fred has hemophilia (X^hY). The probability that their son will inherit the X^h from Susan is 1/2, as he will inherit the Y chromosome from Fred.

James Is a 42-Year-Old Man with Hemophilia, a Sex-Linked Recessive