Mendel's law of segregation states that the alleles of an individual, separate during the formation of gametes.
Mendel crossed a true breeding tall plant (TT) and true breeding short plant (tt). This cross ( F1 generation) yielded only tall plants having a genotype of Tt. He then self-crossed the plants of F1 generation resulting in F2 generation. In the F2 generation, both tall and dwarf plants were found in the ratio of 3:1.
Parents:
True breeding tall plant - TT
True breeding small plant - tt
F1 generation - Tt
So, during the gamete formation both the alleles separate resulting in the formation of gametes; T and t.
F1 generation on self crossing will result in F2 generation.
The punnett square of the second generation is as follows:
T |
t |
|
T |
TT |
Tt |
t |
Tt |
tt |
Phenotypic ratio obtained was 3:1::tall:short