A testcross is a genetic cross between an individual of unknown genotype with a homozygous recessive individual. The purpose of a testcross is to determine the unknown genotype of the individual being tested. If the individual being tested is heterozygous for a particular gene, the offspring of the testcross will show a 1:1 ratio of dominant to recessive traits. If the individual being tested is homozygous dominant, all of the offspring will show the dominant trait. Testcrosses are commonly used in genetics to determine the genotype of an individual.
