In humans, the normal hearing gene (B) dominates the deafness gene and is located in the autosome; the gene for color blindness (color blindness – d) is recessive and linked to the X chromosome. In a family where the mother suffered from deafness, but had normal color vision, and the father with normal hearing (homozygous), color blind, a color blind girl with normal hearing was born. Make a scheme for solving the problem. Determine the genotypes of parents, daughters, possible genotypes of children and the likelihood of future birth in this family of color-blind children with normal hearing and deaf.
from the condition of the problem it is clear that the mother is heterozygous for the deafness gene and homozygous for the blindness gene, and the father has the blindness gene and is heterozygous for the deafness gene. Then the daughter will be homozygous for the gene for blindness and heterozygous for the gene for deafness.
P: (mother) XDXd x (father) XdYBB
daughter – XdXdBb – color blind, normal hearing
Gametes – XDb, Xdb, XdB, YB
Children: HDXdBb – normal vision, normal hearing
XDYBb – normal vision, normal hearing
XdXdBb – color blind, normal hearing
XdYBb – color blind, normal hearing
Cleavage: 1: 1: 1: 1, that is, the probability of having a color blind with normal hearing is 50%, and the probability of having deaf color blind is 0%.