Mendel’s Principles of Genetics

Mendel’s Law:

Observing the consistent pattern of results in the monohybrid crosses. Mendel derived the following three postulates. After their rediscovery, these were described as Laws or Principles of Inheritance.

1. Unit Factors in Pairs: Genetic characters are controlled by unit factors or determiners. These exist in pairs in individual organisms. It means that a tall pea plant has two factors for tallness and a dwarf pea plant has two factors for dwarfness. The F1 hybrid plants have one factor each for tallness and dwarfness, received one from either parent.

2. Dominance and Recessiveness: When two unlike unit factors for a single character are present together in a single individual, one unifying factor is dominant to the other which is said to be recessive. In tall/dwarf characters, tallness is dominant, and dwarfness is recessive.

3. Segregation: During the formation of gametes, the paired unit factors separate or segregate randomly so that each gamete receives one or the other factor with equal likelihood.

It means that from F1 hybrid two types of gametes are formed in almost equal numbers. Each gamete has a 50 percent probability of receiving either the tall or dwarf factor.

4. Independent Assortment: During gametes formation, segregating pairs of unit factors assort independently of each other. It means the segregation of one pair of unit factors isn’t influenced by the simultaneous segregation of other pairs of unit factors. This independent assortment is seen in dihybrid or poly-hybrid crosses.