SAT Subject Biology Practice Question 322: Answer and Explanation
12. Hemophilia is a disorder in which blood fails to clot. John, a male hemophiliac, marries Jane, a normal woman, and together they have four children, two boys (Mark and Mike) and two girls (Molly and Mary). None of the children display the symptoms of hemophilia. Mark, Mike, Molly, and Mary all marry normal individuals and have children. None of Mark's or Mike's children, male or female, display symptoms of hemophilia, but the sons of Molly and Mary all display symptoms of hemophilia while the daughters of Molly and Mary do not.
If one of Mike's daughters marries a normal man, what is the probability that one of their children will display symptoms of hemophilia?
Correct Answer: A
A Because Mike does not carry the gene for hemophilia (see above), he cannot pass it on to his children, and they in turn cannot pass it on to their children.