What is the purpose of performing a test cross?

Consider a tall pea plant with an unidentified genotype.

Tallness predominates over dwarfism in pea plants, however it is unclear if a particular plant is homozygous tall (TT) or heterozygous tall (Tt).

Conducting a test cross can reveal the genotype of the plant.

A plant with an unknown genotype is crossed with a plant that is homozygous for the trait in question in a test cross.

Since every gamete of the recessive homozygous plant carries a recessive allele, the gametes have no effect on the phenotype of the progeny.

By looking at the phenotype of the progeny created in the test cross, we can ascertain the genotype of the specified plant.

The progeny's phenotypes are scrutinized.

Because the phenotypes produced depend on the gametes produced by the plant of unknown genotype, the given plant is homozygous tall (TT) if all the offsprings are tall, and heterozygous tall (Tt) if both tall and dwarf offsprings are produced. The dwarf plant's gametes do not contribute to phenotype because all of them carry the recessive allele 't'.

The purpose of performing a test cross is to determine the genotype of an organism expressing a dominant phenotype.