試題詳解

14. John and Mary are planning to start a family. John was married once before, and he and his first wife had a child with cystic fibrosis. The brother of his current wife, Mary, died of cystic fibrosis. What is the probability that John and Mary will have a baby with cystic fibrosis? (Neither John, Mary, nor their parents have cystic fibrosis.)
(A)1/4
(B)1/6
(C)1/8
(D) 1/12
(E)1/16