Monohybrid Cross Problem Set

Problem 12: 2:1 segregation in Manx cats

Manx cats are heterozygous for a dominant mutation that results in no tails (or very short tails), large hind legs, and a distinctive gait. The mating of two Manx cats yields two Manx kittens for each normal, long-tailed kitten, rather than three-to-one as would be predicted from Mendelian genetics. Therefore, the mutation causing the Manx cat phenotype is likely a(n) __________ allele.

Courtesy of PETNET in Australia

Tutorial

Expected genotype ratio

The expected genotype ratio when two heterozygotes are crossed is 1 (homozygous dominant) : 2 (heterozygous) : 1 (homozygous recessive). When a phenotypic ratio of 2 : 1 is observed, there is probably a lethal allele. Individuals homozygous for the lethal allele (tt in this case) do not survive embryonic development, and are not born. The heterozygotes have a phenotype distinct from normal cats.

The Biology Project
University of Arizona
Thursday, October 1, 1998
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