Jon and Ygritte Snow are planning to have children. Jon has normal vision and is
ID: 316058 • Letter: J
Question
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.
Explanation / Answer
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.
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