Question

In a dog breed known as the Mexican Hairless, the 'hairless' phenotype is a result of a mutation displaying an autosomal dominant pattern of inheritance. Homozygous recessive individuals (hh) display a 'coated' phenotype. Inheriting two copies of the mutation (HH) is lethal during embryonic development. In a cross between two dogs with the hairless phenotype, what proportion of live puppies born are expected to be hairless? Give your answer in the form of a fraction.

Answer 1

Homozygous recessive genotype is hh (coated)

Homozygous dominant genotype is HH (lethal)

Heterozygous genotype is Hh (hairless)

If we cross two heterozygous:

P: Hh x Hh

F1: HH Hh Hh hh

½ of the offspring will be with hairless phenotype

¼ is with coated phenotype

¼ is lethal.