Question 115

Question:

A 28-year-old woman wishing to have a baby for the first time comes to you for genetic counseling. Her husband has no medical problems but her father has hemophilia A. She is worried about the chances of her passing this on to her children. What will you tell her?

Correct Answer: B.  Each of her sons will have a 50% chance of having hemophilia.

Hemophilia A is the classic example of an X-linked recessive disease. Assuming her mate does not have the disease, he will pass on an X to his daughters and a Y to his sons. She will pass either her normal X or her carrier X chromosome to her child, regardless of sex. The daughters therefore have no chance of having the disease, though they may be carriers. Each son has a 50% of developing the disease, depending on which X chromosome he gets from his mom.