Final answer:
A test cross is used to determine whether an individual with a dominant phenotype has a homozygous or heterozygous genotype by crossing it with a homozygous recessive individual. If all offspring show the dominant trait, the parent is homozygous; if there is a 1:1 ratio of traits, the parent is heterozygous.
Step-by-step explanation:
The process of mating an individual expressing a dominant phenotype, but whose genotype is unknown, with an individual expressing the corresponding recessive phenotype, is known as a test cross. This breeding technique allows us to determine whether the unknown parent is homozygous or heterozygous for the dominant trait. If the parent with the dominant phenotype is homozygous, all of the offspring (F1 generation) will exhibit the dominant trait. However, if the parent is heterozygous, there will be a mixed phenotype ratio of 1:1 in the offspring, showing both dominant and recessive traits. This method further supports Mendel's principle that genes are inherited as discrete units and segregate independently during gamete formation.