Final answer:
A test cross is used to determine the genotype of an individual for a dominant trait. By examining the phenotypes of the offspring, we can determine whether the unknown parent is homozygous or heterozygous for the trait.
Step-by-step explanation:
A test cross is a cross between an individual with an unknown genotype for a dominant trait and a homozygous recessive individual.
By examining the phenotypes of the offspring, we can determine whether the unknown parent is homozygous or heterozygous for the dominant trait.
If all the offspring express the dominant trait, then the unknown parent is likely homozygous.
If there is a 1:1 ratio of offspring expressing the dominant trait and offspring expressing the recessive trait, then the unknown parent is likely heterozygous.