1- Tall plant with trait combinaton TT is crossed with a dwarf plant with trait combination tt. This denotes parental generation.
2- T and t are haploid cells. They represent gametes.
3- Fusion of gametes (T and t) gives rise to all tall plants. But they have different trait combination as compared to parents. This denotes F1 generation.
4- During selfing of the F1 generation plants they produce haploid cells each having different trait (T, t, T and t). This represents gametes.
5- New plants are formed in the ratio of 3:1 where 75% are tall and rest 25% are dwarf. This denotes the F2 generation.