SAT Subject Biology Practice Question 323: Answer and Explanation

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Question: 323

13. 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.

Which of the following individuals are heterozygous for hemophilia?

A. John, Mark, and Mike
B. Mark, Mike, Molly, and Mary
C. John and Jane
D. Molly and Mary
E. Mark and Mike

Correct Answer: D

Explanation:

D Mark and Mike do not carry the gene for hemophilia (see solution to 51 above), thus we can eliminate choices A, B, and E. Jane is normal, so choice C is eliminated as well.

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