Test cross

A test cross is a genetic cross, introduced by Gregor Mendel, used to ascertain whether an organism displaying a dominant phenotype is heterozygous or homozygous genotypically. It involves crossing the organism of unknown genotype with an organism that is known to be homozygous-recessive by virtue of its recessive phenotype.

  • If the unknown organism is homozygous, all of the offspring will display the dominant phenotype
  • If the unknown organism is heterozygous, the offspring will segregate with a 1:1 ratio of dominant:recessive phenotypes