In genetics, a test cross, first introduced by Mendel, is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait. Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. If all offspring display the dominant phenotype, the individual in question is homozygous dominant; if the offspring display both dominant and recessive phenotypes, then the individual is heterozygous. In some sources, the “test cross” is defined as being a type of back cross between the recessive homozygote and $F_1$ generation.