Question

How do Mendel's experiments show that the traits may be dominant or recessive?

Answer 1

Mendel used Pea plants to conduct experiments demonstrating the inheritance of characters like height, colour etc. When a tall plant was crossed with a dwarf plant, the progenies of the first-generation were all tall plants. When two of these plants were crossed, the progeny showed three tall and one dwarf plant.
The crosses show that only one T is enough to make the plant tall, that is, it dominates the inheritance of height. Thus, it is called the dominant trait. To make a plant dwarf, both the alleles must be $t$. Thus, it is the recessive trait.