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The phenomenon by which living organisms transmit parental characteristics to their offspring is called heredity. The characteristics of the parents which are transmitted to their offspring are hereditary characteristics. Heredity is also known as inheritance. Hereditary information of organisms is present in the gametes. It is possible for every organism to reproduce their own kind due to the presence of hereditary information in gametes.

Although the offspring closely resemble their parents, they aren’t entirely identical to them. There may be morphological, physiological and behavioristic among the individuals of species. Those differences are known as variation. So, variation can be defined as the differences in the characteristics, or traits, among the individuals of a species. These differences in traits, or variation, is necessary for organic evolution. The branch of science that deals with the study of heredity and variation is called genetics. It can also be defined as the biological science of inheritance.

The term genetics was first coined by W. Batesman in 1905 AD. The first study of genetics was carried out by Austrian Monk Gregor Johann Mendel (1822-1884). He introduced the concept of genes as the basic units of heredity. Mendel carried out his scientific investigation on hybridization of pea plants. He established the laws of inheritance of characteristics in 1865-66 AD. The results of his eight years breeding experiments were read before the “Natural History of Society of Brun (Austria) in 1865 AD. However, his worked remained unnoticed until 1900 AD. Mendel died in 1884 AD before he could see his work accepted and appreciated.


Gregor Mendel conducted his experiments over a period of eight years on the common edible garden pea plant (Pisum Sativum) in his monastery garden at Brunn, Austria. Mendel Chose pea plant for his experiment due to these reasons: -

  • Easy to grow in the garden.
  • The flowers of pea plants are hermaphrodite, i.e flowers have bisexual characteristics.
  • Easy to obtain pure breed plant through self-fertilization
  • The generation time of pea plants is less.
  • They have excellent disease resistance and have an optimal rate of survival.

The seven pair of contrasting characteristics of pea plant that Mendel studied were:

·         Pea shape (round or wrinkled)

·         Pea color (green or yellow)

·         Pod shape (constricted or inflated)

·         Pod color (green or yellow)

·         Flower color (purple or white)

·         Plant size (tall or dwarf)

·         Position of flowers (axial or terminal)



Mendel had idea that a pea plant inherits two genes of information for  a single characteristic, one from each parent in each generation. So, he selected seven pairs of contrasting characteristics of a garden pea plant. The process of his experiment was:

1.       Snipped off anthers(male parts)

2.       Dusted stigma with pollen grains.

3.       Covered flowers with bags to avoid further pollen grains to fall into it.

His experiment can be demonstrated as follows: -


1.       Mendel’s first law: law of dominance

It states that, “In crossing between pure organisms having contrasting pair of characteristics of a pair, only one character appears in the first filial generation.”

2.       Mendel’s Second law: Law of segregation

Mendel's Law of Segregation states that, "a diploid organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent."

3.       Mendel’s Third Law: law of independent assortment

Mendel's law of independent assortment states that, “genes do not influence each other with regard to the sorting of alleles into gametes; every possible combination of alleles for every gene is equally likely to occur.”