A pregnant woman with recessive X- linked hemophilia and whose partner is a normal (non hemophiliac) man wants to know the chances that she will have an affected child. From an ultrasound, she knows that the child is a boy. What are the chances that her son will have hemophilia?

Question

Quizplus · Accepted Answer

Since hemophilia is an X-linked recessive disorder, a son inherits his X chromosome from his mother and his Y chromosome from his father. If the mother is a carrier of the hemophilia gene (which she must be to be considered "affected" by the question's context), there is a 100% chance that her son will inherit the X chromosome carrying the hemophilia gene, as he can only inherit an X chromosome from her and she only has affected X chromosomes to pass on.

A Pregnant Woman with Recessive X- Linked Hemophilia and Whose