A test cross is a term used in genetics. It was first devised by Gregor Mendel, the father of modern genetics. A test cross involves mating an organism with a dominant trait with an organism with a recessive trait and studying the offspring. The point of this is to find the type of genotype of the dominant trait (or phenotype). If the offspring all contain the dominant phenotype, then the corresponding genotype is homozygous, meaning that the alleles of the gene are identical. If any of the offspring contains the recessive phenotype, then the corresponding genotype is heterozygous, meaning that the alleles of the gene are different. An animal breeder might be interested in performing a test cross to determine the genetic purity of a particular breed of animal.