Question

The Manx phenotype in cats is caused by an autosomal dominant allele that is lethal in the homozygous state. Cats that are homozygous recessive have a normal tail. A female Manx cat mates with a male Manx cat. What percentage of the offspring is expected to have normal tails?

Answer 1

When mating two Manx heterozygous cats, 33.3 percent of the surviving offspring are expected to inherit homozygous recessive alleles (mm) and therefore, will exhibit a normal tailed phenotype.

Step-by-step explanation:

The Manx phenotype in cats is an example of a dominant lethal inheritance pattern, where the autosomal dominant allele causes Manx (a tailless condition) but is lethal in the homozygous state. Since both parents are Manx, they are heterozygous for the trait (Mm). When two heterozygous individuals mate, the typical Mendelian genotypic ratio would be 1:2:1. However, with the lethal allele present, the homozygous dominant (MM) genotype is not viable, leaving only three possible genotypes: MM (non-viable), Mm (Manx), and mm (normal tail).

The expected ratio among the surviving offspring is therefore 2:1, where two out of three surviving cats are heterozygous Manx (Mm) and one out of three is homozygous recessive (mm) with a normal tail. Therefore, 33.3 percent of the kittens are expected to have normal tails.