Mendel's Law Of Inheritance

The credit for our present understanding of the mechanism of heredity goes to an Austrian monk, Gregor Johann Mendel. He performed a large number of experiments on pea plant and deduced his observation to mathematical laws. These laws are called Mendel's Laws Of Inheritance or Mendelism. Due to his achievements, he is also known as Father of Genetics.




Mendel's Experiments

Mendel carried out his experiments on the common garden pea, Pisum Sativium for seven years (1856-1863), in his monastery garden. He procured seeds of 34 different varieties of peas from the local seedsman and grew them in the garden. 

He chose garden pea as plant material for his experiments due to the following reasons :
  1. Peas are available in many pure breeding varieties with observable alternatives form for a trait or characteristics.
  2. Pea flowers are bisexual.
  3. Peas are self-pollinating as such the possibility of the introduction of outside genetical influences was eliminated.
  4. hybrids resulting from crossing two varieties were perfectly fertile.
  5. Pea plants have a short life span.

Mendel's Laws of Inheritance

Based on the observation of his experiments on a garden pea, Mendel drew some important conclusions, Known as Mendel's Laws of Inheritance.




Mendel's Law of Dominance

The law of dominance states that when two alternative forms of a trait are present in an organism, only one factor expresses itself in F1 generation progeny and is called dominant, while the other that remains covered is called recessive.

The law of Dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the F1 generation and the expression both in the F2 generation.


Mendel's Law of Segregation

Mendel's law of segregation states that when a pair of allelomorphs are brought together in the hybrid (F1), they remain together in the hybrid without blending but separate complete and pure during gamete formation. This law is also known as Mendel's second law or law of purity of gametes. It sometimes said to be the law of the splitting of hybrids.



The law of segregation can be explained as follows: pure breeding red (RR) and white (rr) varieties when crossed in F1 generation form Hybrid red (Rr). During the gamete formation segregation takes place and only one factor of the pair of alleles alone enters one gamete and the other enters to other gametes. Thus a gamete can be only either R or r. After self-pollination, they result in RR, Rr, Rr, rr plants in the F2 generation. Each parent thus produces two types of gametes which have equal chances of combining together.


Mendel's Law of Independent Assortment

Mendel's independent assortment can be defined as that when two pairs of independent alleles are brought together in the hybrid F1, they show independent dominant effects. In the formation of gametes, the law of segregation operates, but the factors assort themselves independently at random freely. It is immaterial whether both dominant characters enter the hybrid from the same or two different parents but the segregation and assortment remain the same.




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