Mendel put forward three important laws based on his experiments with pea plants. These are:
i) Law of dominance - It states that one factor in a pair may mask or prevent the expression of the other. The variety that appeared in the F1 generation is dominant and those which did not appear in the F1 generation is recessive
For example in pea plant, the height is controlled by a pair of factors or genes (T or t). If Tt is present, the plant would be tall since tallness is dominant over shortness.
ii) Law of segregation - During gamete formation the genes of a particular character separate and enter different gametes. This is the law of segregation. This law is also called law of purity of gametes.
Example: During gamete formation the paired factors (Tt) present in the F1 plant segregate independently and enter different gametes. So each gamete receives either T or t from the paired factors Tt, which are responsible for the expression of a single character.
iii) Law of independent assortment - This law is based on dihybrid experiment. According to this law, the genes for each pair of characters separate independently from those of other characters during gamete formation.
Example: Consider a plant with yellow round seeds being crossed with another pea plant with green wrinkled seeds. During gamete formation of a dihybrid cross, the factors for yellow colour assort out independently of the factors for round shape.
The gene Y may combine with the dominant gene R or the recessive gene r of the other character and enter a gamete. In the same way, the gene y may combine with the dominant gene R or the recessive gene r and enter a gamete. So the F1 dihybrid plants produce four types of gametes and they are YR, Yr, yR and yr.