Answer to Question #147146 in Genetics for Vaith

Question

In a human, polydactyly is autosome dominant disease. The blood groups of system ABO are determined by three allelic genes: i0, IA, IB. The blood groups of a human being are i0i0 - I(0); IAIA or IAi0 - II(A); IBIB or IBi0 - III(B); IAIB - IV(AB). In a family, a mother had I blood group and polydactyly, the father had IV blood group and normal structure of hand. There was born a child with first blood group and normal structure of hand. Determine the parental genotypes and the probability of a child with III blood group and polydactyly.

Answer 1

Since polydactyly is a dominant gene hence would express both in heterozygous and homozygous forms, the mother's genotype will be iOPp for a polydactyl structure of hands and the father's IAIBpp, for normal structure of hands.

The probability of finding a blood group III from a cross of the two parents will be 1/2, that is 0.5.