Imagine that you are a genetic counselor, and a couple planning to start a family comes to you for information. Charles was married once before, and he and his first wife had a child with cystic fibrosis. The brother of his current wife, Elaine, died of cystic fibrosis. What is the probability that Charles and Elaine will have a baby with cystic fibrosis

1/6

Explanation:

Assuming the disorder is not sex linked, Charles is a carrier so he will be Ff.

His wife Elaine can be a carrier or not because her parents must have been both Ff

Possible F1 generation for her was FF, Ff, Ff and ff. She does not have the disease.

Therefore the total chance of her having FF was 1/3 whereas Ff will be 2/3

Probability of the kid having the disease will be calculated by;

(2/3*1/4) + (1/3*0) = 1/6