A tall true breeding garden pea plant is crossed with a dwarf true breeding garden pea plant. When the ${\mathrm{F}}_1$ plants were selfed the resulting genotypes were in the ratio

Mendel did the crossing of pure tall plant represented by (TT) with a pure dwarf plant represented by (tt). In the F₁ generation of this cross, plants formed are tall (Tt). When this plant from F₁ generation undergoes self-pollination, then in the F₂ generation, three tall plants and one dwarf plants are seen. In this 1 homozygous tall plant (TT), two heterozygous tall plants(Tt), 1 homozygous dwarf plant(tt) are formed. Phenotypic ratio is 3:1::Tall:Dwarf, while the genotypic ratio becomes 1:2:1::Tall homozygous : Tall heterozygous : Dwarf