Crossing an organism with dominant genotype to a recessive homozygote for a specific phenotype in order to determine dominance/recessiveness of the unknown genotype and the pattern of inheritance based on the phenotype of each progeny
Test cross is first introduced by Gregor Mendel, the Father of Modern Genetics. He made use of the test cross to identify the genotypes responsible for the phenotypes of the progenies after a cross.
This means that a test cross is made between an organism exhibiting the dominant trait (and thus carrying the unknown dominant genotype) and another organism displaying the recessive trait.
If the recessive trait is manifested in any of their progenies it means that the unknown genotype is heterozygous dominant. In contrast, if the dominant trait is observed in all progenies the unknown genotype is homozygous dominant.
The accuracy the test cross results will therefore depend on the availability of a large statistical sample.