Question

Alan has hemophilia A. His sister, Alice, has one son, Blaine. Blaine also has hemophilia A. Alan and his wife Annette have 2 children, Bart and Barbara. Barbara has a daughter, Cassie, and a son Chip. Cassie and Blaine are married and have a son, Daniel, with hemophilia A. They are now expecting fraternal twins, a boy and a girl.

What is Cassie and Blain's son's (the fraternal twin) risk to have hemophilia A?
(A) 0%
(B) 25%
(C) 50%
(D) 75%
(E) 100%

Answer 1

Cassie and Blaine's new son has a 50% chance of inheriting hemophilia A because it is an X-linked recessive condition and Cassie is a carrier of the affected gene.

Step-by-step explanation:

Hemophilia A is a genetic disorder linked to the X chromosome, affecting the body's ability to clot blood. In the scenario where Cassie and Blaine, who have a son, Daniel, with hemophilia A, are expecting fraternal twins, we must evaluate the risk of the newborn son having hemophilia A. Since hemophilia is an X-linked recessive condition, males inherit this condition from their carrier mothers.

Cassie must be a carrier of hemophilia A because her father, Blaine, has the disorder and her mother must have been a carrier. Therefore, she carries one affected X chromosome. Since sons receive their X chromosome from their mothers, there is a 50% chance that their son will inherit the affected X chromosome and therefore have hemophilia A.