Testcross is a genetic term that refers to the cross between an individual with unknown genotype and a homozygous recessive individual. It is commonly used in genetics to determine the genotype of an individual by mating it with a known homozygous recessive individual. Synonyms for testcross include backcross, differential test, and test mating. The backcross is a similar term that refers to the mating of a hybrid offspring with one of its parents. Differential test and test mating are also used in a similar context to test the genetic makeup of an individual. These terms are essential tools in genetics, allowing researchers to uncover hidden traits and determine the composition of an individual's genes.