The gene ‘T’ for the character of tallness in pea plant is dominant and gene ‘t’ is recessive. Explain it on the basis of Mendel’s experiment.

Explanation

Mendel selected garden pea plant (Pisum sativum) as an experimental material. The pea plant shows various characters and atleast two contrasting expressions for each of the characters.
Mendel selected height of the pea plant. The two contrasting expressions for the height of pea plants are tall plants and short plants.
Mendel crossed the tall parent (P) plant, (TT), with another short parent (P) plant (tt), and obtained all tall plants in `F_(1)` generation. None of the short plants were produced in `F_(1)` generation. They were also not of medium height. It means that only one parental characteristic was expressed in the offsprings.
When the plants of `F_(1)` generation were allowed to self-pollinate, about `75%` plants were tall and about `25 %` were short in the `F_(2)` generation. Thus, the genes for tallness and shortness both are capable of being inherited from the parents of `F_(1)` generation.
This indicates that both the tallness and shortness traits were inherited in the `F_(1)` plants, but only the tallness trait was expressed.
This led Mendel to propose that two copies of factor (gene) controlling traits are present in sexually reproducing organism.
These two may be identical or may be different.

This experiment indicates that the genes TT or genes Tt is the genetic constitution for tall plants while tt for the short plant. It means that only presence of gene T is responsible for the expression of tallness while the absence of dominant gene T and tt genes produces shortness.
Thus, tallness in pea plant is the dominant trait and shortness is the recessive trait.