Define and design a test-cross.

Crossing of F₁ individual dominant phenotype with its homozygous recessive parent is called test cross. Test cross is used to know the genotype of F₁ dominant phenotype.
Example: 1. When a tall plant (TT) is crossed with dwarf plant (tt) in F₁ progeny all plants will be tall.
2. A tall plant can be of homozygous or heterozygous.
3. To know genotype of F₁ progeny, F₁ is crossed with recessive plant.
4. After crossing if progeny are with 1:1 ratio of tall and dwarf plants, then F₁ will be heterozygous.