Genetics: Laws of Inheritance | Principles of Mendelian Inheritance

In this article we will discuss about:- Laws of Inheritance or Principles of Mendelian Inheritance

The results obtained by Mendel were studied and on their basis he proposed certain laws known as “Laws of heredity”.  These laws are discussed below:

1)  Law of dominance:

This law states that when two contrasting genes for a character come together in an organism, only one is expressed externally and shows visible effect.  It is called dominant and the other gene of the pair which does not express and remains hidden is called recessive.

2)  Law of segregation or Purity of gametes:

This law states that both parental alleles (recessive and dominant) separate and are expressed phenotypically in F2 generation.  When F2 generation was produced by allowing F1 hybrid to self pollinate, to find out segregation or separation it was observed that both dominant and recessive plants appeared in 3:1 ratio.  

3)  Law of Independent assortment:

The law of independent assortment states that when inheritance of two or more genes occur at one time, their distribution in the gametes and in the progeny of subsequent generations is independent of each other.  To prove this, he did a dihybrid cross.  He crossed homozygous dominant smooth and yellow seeded (YYRR) with homozygous recessive wrinkled and green seeded (yyrr) plants. The F1 hybrid was self pollinated and F2 generation was obtained with the phenotypic ratio of 9:3:3:1 and genotypic ratio of 1:2:1:2:4:2:1:2:1.