Mendel's Law: Dominance ,Segregation, Independent Assortment

In this article we will discuss about Mendel's Law of inheritence -

1. Law of Dominance (first law) :

This law states that when two opposite forms of a trait(genes) or character are present in an organism, only one factor expresses itself in F1-progeny and is called dominant, while the other that remains masked is called recessive

Law of Segregation (second law):

This law of Segregation states that during gamete formation alleles segregate or separate from each other and pass on to different gametes in equal number. The different genes segregate from each other in a pure form, pass on to different gametes formed by a hybrid and then go to different individuals in the offspring of the hybrid.

Salient features of Law of Segregation:

1) After crossing between two plants having contrasting characters, they do not mix or blend together.

2)Law of segregation is also known as law of purity of gametes.Because the gamates remain together in pure form without affecting each other.

3) Segregation of two alleles of a gene during gamete formation takes place usually due to the separation of homologous chromosomes.

4) Segregation leads to phenotypic ratio of 3 : 1 in F2 for characters controlled by single gene, and 9:3:3:1 ratio for two genes.

Law of Independent Assortment (third law):

This Law states that during a dihybrid cross , an assortment of each pair of traits is independent of the other.That means, independently one pair of trait segregates from another pair of traits during gamete formation . Mendel’s always portrayed his experiment that the combinations of traits of the progeny are always different from their parental traits. He based on this, formulated the Law of Independent Assortment

If dihybrid crosses done between the parental genotype rryy (green wrinkled seeds and RRYY (round yellow seeds) .Then the chances of formation of gametes with the gene R and the gene r are 50:50, with the gene Y and the gene y are 50:50. Law of Independent Assortment states that the segregation or separation of Y and y is independent of the segregation of R and r. At a results four types of gametes are formed - rY, ry RY, and Ry. These four types of combinations of alleles are different from their parental combination of alleles.