Mutations in the DFNB1 gene cause hearing loss. The D allele is dominant to the

Question

Mutations in the DFNB1 gene cause hearing loss. The D allele is dominant to the d allele. Two individuals with normal hearing, both heterozygous for a mutation in the DFNB1 gene, have children together.

Draw a Punnett square illustrating this cross.

What is the genotypic ratio seen in the children?

What is the phenotypic ratio seen in the children?

Many years later, one of the children, Jody, takes a mate who has hearing loss due to DFNB1. They have two children with normal hearing and two children with hearing loss.

i)    What is Jody’s phenotype?


ii)   What is Jody’s genotype?


iii)  How do you know Jody’s phenotype and genotype?

Explanation / Answer

1. Cross between two heterozygous for a mutation in the DFNB1 gene will have the children with the following genotypes.

Dd* Dd = DD, Dd, Dd, dd.

Means, 25% (DD) are normal hearing, 50% (dD) are carriers and another 25% (dd) are affected.

The genotypic and phenotypic ratio = 1: 2: 1 (Normal: carriers: affceted)

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