Suppose that a woman with normal blood clotting mates with a man who also has normal blood clotting, and that their first child is a boy who has X-linked hemophilia. Which statement best predicts the outcomes of their mating?

Question

Quizplus · Accepted Answer

Hemophilia is an X-linked recessive disorder. Since the son has hemophilia, his mother must be a carrier (XHXh), and the father is normal (XHY). Daughters receive an X chromosome from each parent, so they will not have hemophilia unless they receive the affected X from their mother (which is a 50% chance per pregnancy, but they need two affected alleles to express the condition, and they always receive a normal X from their father). Sons receive the Y chromosome from their father and an X chromosome from their mother, so they have a 50% chance of inheriting hemophilia if they inherit the affected X from their mother. Therefore, half the boys (sons) could have hemophilia, but the girls, receiving one X from each parent, will not express the condition (as they receive at least one normal X from their father).

Suppose That a Woman with Normal Blood Clotting Mates with a Man