Question

A man is heterozygous for cystic fibrosis (an autosomal recessive disorder). His partner, however, is homozygous for the healthy gene, meaning she is not a carrier. What are the odds that their child will have the disease cystic fibrosis?

Answer 1

Answer: O%

Explanation:

Let dominant allele for cystic fibrosis be represented by H

Let recessive allele for cystic fibrosis be represented by h

The man is heterozygous for it so his genotype will be Hh

His partner is homozygous for the healthy variant i.e. for the wild type allele so her genotype will be HH

If they have a child:

Hh X HH :

          H      h

H     HH    Hh

H     HH    Hh

50 % of children will be homozygous for the healthy variant of allele and 50% will be heterozygous for it. Phenotypically they all will be healthy and not have cystic fibrosis since H is dominant over h.

Hence, 0% of children will have cystic fibrosis.