Jon and Ygritte Snow are planning to have children Jon has n

Jon and Ygritte Snow are planning to have children. Jon has normal vision and is heterozygous for the cystic fibrosis (CF) gene. Ygritte has red-green color blindness and is also heterozygous for the CF gene. What is the chance that they will have a child with red-green color blindness AND cystic fibrosis?

(A) 50% of all children will have both conditions, regardless of gender.

(B) 25% of all children will have both conditions, regardless of gender.

(C) No children will have both conditions.

(D) No daughters will have both conditions but 25% of the sons will.

There is not enough information to determine the genotypes of the parents.

Solution

Answer - Option D - No daughters will have both conditions but 25% of the sons will.

Because Jon is normal all the daughters will be heterozygous for color blindness and sons will be affected. Since both the parents are heterozygous for CF 50% of the children will be homozygous and will have cystic fibrosis. Hence the answer is option D.