Test (back) cross

The genotypes TT and Tt both produce a tall phenotype. In order to establish the genotype, a test cross is used.

The organism in question is crossed with a homozygous recessive individual (tt).

Genetics back cross 1

If no short plants (tt) are produced in the offspring the unknown parent was homozygous (TT).

Genetics back cross 2

If any short plants (tt) are present in the offspring the unknown parent was heterozygous (Tt).