To determine the genotype or the types of gametes produced by an individual showing a dominant phenotype (or a hybrid like AaBb), a test cross is performed. a typical test cross involves crossing the organism with the recessive parent (homozygous recessive) . For a dihybrid genotype AaBb, the corresponding homozygous recessive genotype is aabb. This cross ensures that the phenotypes of the offspring directly reflect the gametes produced by the parent being tested.