Suppose that you are a genetic counsellor, and a couple comes to you with concerns that if they have a child together, it could have hemophilia. Suppose also that neither one of them has hemophilia, but the woman's biological father did have an X-linked recessive form of hemophilia. Which of the following is the best advice you could give them?

Question

Quizplus · Accepted Answer

Hemophilia is an X-linked recessive condition. Since the woman's father had hemophilia, she must have one affected X chromosome (making her a carrier) because she inherited an X chromosome from her father. The man cannot pass an X chromosome to his sons (only Y chromosomes), so sons have a 50% chance of inheriting the affected X from their mother and having hemophilia. Daughters receive one X from their mother and one from their father, so they will not have hemophilia (since it requires two affected X chromosomes for a female to express the condition) but have a 50% chance of being carriers like their mother.

Suppose That You Are a Genetic Counsellor, and a Couple