What is a test cross?

A test cross is a genetic technique used to determine the genotype of an individual that exhibits a dominant phenotype. This is achieved by crossing the individual in question with a homozygous recessive individual. Since the recessive homozygous individual can only contribute recessive alleles to the offspring, the phenotypes of the resulting offspring reveal the genotype of the dominant individual. If any offspring exhibit the recessive phenotype, it indicates that the dominant individual must be heterozygous (carrying one dominant and one recessive allele). If all offspring display the dominant phenotype, this indicates that the individual is homozygous dominant (having two dominant alleles).

This method is fundamental in genetic studies as it provides clarity on the inheritance patterns of traits and is widely utilized in breeding experiments and understanding the basics of Mendelian genetics.