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
答案是B
我的想法是
John是Tt，Mary是TT或Tt，所以不是1/2×1/4=1/8吗!?
先谢谢各位大大~~