Law of Segregation:
The law of segregation states that ‘when a pair of contrasting factors or genes or allelomorphs are brought together in a heterozygote (hybrid) the two members of the allelic pair remain together without being contaminated and when gametes are formed from the hybrid the two separate out from each other and only one enters each gamete’.
Mendel explained above the results by presuming that:
1. Tallness and dwarfness are determined by a pair of contrasting factors or determiners called genes. A plant is tall because it possesses determiners for tallness (represented by T) and a plant is a dwarf because it has determiners for dwarfness (represented by t).
2. These determiners occur in pairs and are received from either parent.
3. When two factors for alternative expressions of a trait (T and t) are brought together by fertilization, only one (the dominant trait for tallness) expresses itself masking the expression of the other (the recessive trait, dwarfness). On the basis of this behavior, tallness is described as a dominant character and dwarfness as recessive (law of dominance and recessiveness).
4. The determiners are never contaminated. When gametes are formed, these unit factors segregate so that each gamete gets only one of the two alternative factors. It means factors for tallness (T) and dwarfness (t) are separate entities and in a gamete either T or t is present. When F1 hybrids (Tt) are self-polinated the two entities separate out and unite independently producing tall and dwarf plants (law of segregation).