It is known that cataracts and redheads in humans are controlled by a dominant gene.

It is known that cataracts and redheads in humans are controlled by a dominant gene. A red-haired woman who does not have cataracts married a light-haired man who had recently undergone cataract surgery. Determine what kind of children these spouses can have, if you keep in mind that the man’s mother has the same phenotype as his wife.

Let’s designate the gene that causes the development of cataracts in a person as S, then the gene that causes the absence of this disease will be designated s.

Let’s designate the gene for red hair as K, then the gene for light hair will be k.

A fair-haired man is homozygous on the basis of hair color – kk, because otherwise this trait could not be realized in his phenotype. Consequently, his red-haired mother is heterozygous for the gene that determines hair color. Since it is said in the problem statement that the wife and mother of the husband have the same genotype, we will write down the genotype of the wife as follows – ssKk. This woman produces two types of eggs – sK, sk.

Since the man’s mother could not pass on the S cataract gene to him, the man is therefore heterozygous for this gene. Its genotype is thus Sskk. It is capable of producing two types of spermatozoa – Sk, sk.

All possible offspring from the marriage of the described man and woman will be represented by the following options:

children with red hair and cataracts (2SsKk) – 50%;

children with blond hair and cataracts (Sskk) – 25%;

children with fair hair, not suffering from cataracts (sskk) – 25%.