Question

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

Answer 1

The correct option is D Molly and Mary

Hemophilia is sex linked recessive disorder. Gene responsible for it present on X chromosome and only expresses in dominant state. Out of four children of john (hemophiliac male) and Jane (normal woman), both the girls Molly and Mary become heterozygous for hemophilia as they got hemophiliac X chromosome from father only, which they pass on to their children resulting sons with hemophilia expressed and daughters are either normal heterozygous for hemophilia. The boys Mark and Mike are normal as they don't get hemophiliac X chromosome from father and when they married with normal individuals, all their children would be normal. Thus, the correct answer is ' Molly and Mary.'