Generally a Test cross involving an individual with a homozygous recessive trait . When a single trait is being studies, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (either homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous for a trait, then approximately half of the offspring will display the recessive phenotype. If all the offspring carry dominant phenotype, Then the unknown genotype is homozygous.
