In humans, dark hair color completely dominates over light, and normal hearing over congenital deafness

In humans, dark hair color completely dominates over light, and normal hearing over congenital deafness. A fair-haired man, deaf from birth, has a dark-haired son with normal hearing and a daughter with blond hair, who manifested hereditary deafness. Set the genotype of the mother of these children. What is the probability of having a child with a mother phenotype in this family?

We introduce the notation of genes:
A – dark hair;
a – fair hair;
B – normal hearing;
b – congenital deafness.
– Set the genotypes of the parents. The genotype of a fair-haired deaf father is obvious: aabb.
This family has a dark-haired son with normal hearing: A – B–. He could not inherit the dominant genes A and B from his father, which means he received them from his mother. The blonde deaf daughter aabb inherited from the father and mother one recessive gene from each allelic pair.
Therefore, we can conclude that the mother of these children is digeterozygous: AaBb, has dark hair and normal hearing.
Thus, the probability of having a dark-haired child with normal hearing (maternal phenotype) is 25%.
Answer: Mother is diheterozygous, the probability of having a baby with a mother phenotype is 25%.

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