What Is a Test Cross?

A test cross is an important technique in breeding analysis where an organism having a dominant phenotype and an undetermined genotype is crossed with a homozygous recessive organism. The purpose of a test cross is to identify whether the unknown genotype is heterozygous or homozygous dominant.

The test cross was a method devised by Gregor Mendel, one of the pioneering scientists in the field of genetics. An organism's phenotype is the perceived traits or observable expression of the genotype, which refers to the organism's genetic composition. An expression of a dominant phenotype in an individual results in an unknown genotype. During a test cross, if an offspring exhibits a recessive phenotype, then the organism has a heterozygous genotype, containing two different alleles for a specific characteristic.