Definitions for "Testcross"
a genetic test to determinethe zygosity of an unknown individual by crossing it with a homozygous recessive individual.
breeding of an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype based on the phenotypic ratios of the offspring
A cross of an individual of unknown genotype or a heterozygote (or a multiple heterozygote) with a tester individual.