State and explain Mendel's laws of inheritance.

Explanation

Based on Mendel.s observations, the German scientist Carl Correns formulated certain principles of heredity. These now known as Mendel.s laws of inheritance or the principles or laws of inheritance. These are
(a) Law of dominance It states that when two contrasting pure alleles for a character come together through cross in an organism of `F_(1)`-generation, only one is expressed completely and shows visible effect. This allele is called dominant and the other allele of the pair which does not express and remains hidden is called recessive. For example, in the monohybrid cross, when dwarf plant is crossed with tall plant, in the `F_(1)`-generation are all tall plants. This shows that allele for tallness is dominant.
(b) Law of segregation This principle states that, though the parents contain two alleles during gamete formation, the factors or alleles of a pair of trait segregate from each other, such that a gamete receives only one of the two factors. Hence, the alleles do not show any blending and both the characters are recovered as such in the `F_(2)` -generation, though one of these is not seen in the `F_(1)` generation.
(c) Law of independent assortment It states that when two or more pairs of traits are combined in a hybrid, segregation of one pair of traits is independent to the other pair of traits. As in the dihybrid cross of Mendel the presence of new combinations, i.e. round-green and wrinkled -yellow suggests that the genes for shape of séed and colour of seed are assorted independently. The results `(9:3:3:1)`, indicate that yellow and green seeds appear in the ratio of `9+3:3+1=3:1`. Similarly, the round and wrinkled seeds appear in the ratio of `9+3:3+1=3:1`.
This indicates that each of the two pairs of alternative characters viz yellow-green cotyledon colour is inherited independent of the round-wrinkled characters of the cotyledons.