In humans, the gene for congenital deaf-dumbness is recessive in relation to the gene for normal hearing.

In humans, the gene for congenital deaf-dumbness is recessive in relation to the gene for normal hearing. From the marriage of a deaf-mute woman with a man of normal hearing, a deaf-mute child was born. Determine the genotypes of all family members. What is the segregation by genotype and phenotype?

Let’s designate a gene that is recessive and causes the development of deaf-dumbness in humans as l. The corresponding gene for normal hearing will be designated L.

The woman, according to the condition, suffers from deaf-dumbness. Let us write it ll, because only under the condition of homozygosity the recessive gene has the ability to be phenotypically realized. This woman produces eggs of the same type – l – containing.

A deaf-mute child, like a mother, carries in his genotype 2 deaf-mute genes – ll, one of which he inherits from a deaf-mute mother, the second from a normally hearing father. The father is a heterozygous healthy carrier of this gene. Let’s write it Ll, and the spermatozoa produced by it – l and L.

This couple has a 50% chance of having a normal hearing child (Ll).

The probability of having a deaf-mute baby (ll) is 50%.

Splitting by genotype, thus – 1: 1, by phenotype – also 1: 1.