In a deaf-mute (it is assumed that deaf-dumbness is hereditary) of a blue-eyed man

In a deaf-mute (it is assumed that deaf-dumbness is hereditary) of a blue-eyed man, all children are brown-eyed and have normal hearing and speech. What signs should the mother of these children bear and what genotype could she be if they had a blue-eyed child with a deaf-mute?

Let us designate the gene responsible for the development of deaf-dumbness in a person as b, then the gene that determines the development of normal hearing and the ability to speak will be B.

Since all the children of the blue-eyed father are brown-eyed, we conclude that the brown-eyed gene is dominant and denote it as C, then the blue-eyed gene will be c.

The blue-eyed deaf-mute father, according to the designations, will be written as bbcc, he will produce the same type of spermatozoa bc.

In order for all children in this family to have normal hearing and brown eyes, the mother must be a homozygote for genes of dominant traits – ВВСС and produce the same type of eggs – BC. Then all children will be BbCc, which will correspond to the resulting phenotypes.

A blue-eyed deaf-mute child would, like the father, be recorded as bbcc. The mother of such a child had to pass on both recessive genes to him, therefore, she either herself had to be deaf and blue-eyed – bbcc, or a woman with normal hearing and brown eyes – BbCc, diheterozygous for both of the considered characteristics. In the latter case, she would produce germ cells BC, bc, bC, Bc and the following children could be born to this married couple:

with normal hearing and brown eye color (BbCc) – 25%;

deaf and dumb with blue eyes (bbcc) – 25%;

deaf and dumb with brown eyes (bbCc) – 25%;

with normal hearing and blue eye color (Bbcc) – 25%.