Law of Segregation
Definition
This law states that the two alleles during the formation of gametes or spores by meiosis move apart due to separation of the homologous chromosomes , so that each gamete or spore receives only one allele of each character, they are always pure . The law of Segregation is , therefore, also called the law of purity of gametes/spores.
Explanation:-
The law of Segregation can be explained with the help of monohybrid cross:-
Cross between pea 🫛 plant
Select a pure tall pea plant and cross it with a pure dwarf pea plant. Here, the tall size is dominant over the dwarf size. The allele equipment of these parent plants may be represented by TT and tt, where T stands for the allele of dominant tall size and t for the allele of recessive dwarf size. During gamete formation, meiosis segregates (separate) the allele of tallness and dwarfness so that the gametes get the allele T and t respectively.
The F1 offspring formed by the fusion of gamete with alleles T and t will have two unlike allele Tt for the size. The allele for tallness, being dominant, will express itself in F1 plants, and the allele for dwarfness, being recessive, will remain unexpressed. All the F1 plants are therefore tall.
Now cross the hybrid plant of F1 generation . Half of the gametes receive the allele T for tallness and the half get the allele t for dwarfness in each parent. A gamete with allele T has an equal chance for fusing with a gamete having allele T or t. Therefore, F2 plants have three kinds of genotype: TT, Tt and tt. In F2 generation, The ratio will be 1:2:1 in genotype and 3:1 in phenotype.
These ratios are possible only if-
I) the two alleles of a trait do not affect each other when together
II) segregate during gametogenesis,
III) gametes contain only a single allele of a trait
IV) the allele come together in the offspring by random fusion of the gametes
V) F1 plants are hybrid, having contrasting allele (Tt here)
