A man and a woman are both deaf due to being homozygous for a recessive autosomal mutant allele. However, they are homozygous recessive at different gene loci. If all their children have normal hearing, which event has occurred within each child?

Answer: Children inherit one maternal allele and one paternal allele from each loci.

Explanation:

A homozygote is a gene that has two identical copies for a given trait on the corresponding two chromosomes. A homozygous dominant genotype arises when a given sequence encompasses two alleles for the dominant attribute. And a homozygous recessive organism carries two copies of the same recessive allele.

The autosomal dominant inheritance pattern occurs when the altered allele is dominant over the normal one and only one copy is needed for the disease to be expressed. Since it is autosomal, the gene is found in one of the 22 pairs of non-sexual chromosomes, or autosomes, and can equally affect sons and daughters.

In this example, the woman and man have two recessive alleles which cause the deafness. But, those mutations are found at different gene loci, this means they are different causes for the deafness.

If children have normal hearing, it is because they only have one recessive allele from each parent. Because, children inherit one maternal allele and one paternal allele from each loci. So, since each parent has two recessive genes but in different loci (for example, let's call it maternal loci M and paternal loci P, with the alleles mm and pp respectively). The child inherits only one defective maternal allele (m) and one defective paternal allele (p). But they are not found in the same part of the chromosome. The other two alleles for that section of the chromosome are nomal (dominant) And since a recessive allele does not become a trait unless both copies of the gene are recessive, all of their children have normal hearing.

Complementation

Explanation:

The children are able to hear because the deaf man and woman carry different homozygous recessive mutations that have resulted in the same phenotype i. e. deafness. As a result, the same mutant phenotype results in children with the wild-type phenotype (hearing), when crossed.