Genetics : A study of heredity and variation

The term 'Genetics' was used for the first time by W. Bateson in 1905, although beginning of the science of genetics was made in 1900 by rediscovery of Mendel's work (consult next main topic). Genetics is often described as a science which deals with heredity and variation, Heredity includes those traits or characteristics which are transmitted from generation to generation and is, therefore, fixed for a particular individual. Variations on the other hand, are mainly of two types, namely (i) hereditary and (ii) environmental. Hereditary variations refer to differences in inherited traits. Such variations are found not only in progenies of different parents but also among progeny from the same parents. Traits which are present in parents can reassort and give rise to different combinations, which are responsible for hereditary variations within the same progeny. Identical twins, however, is an exception, where no hereditary variation exists. Environmental variations are those which are merely due to environment. Study of genetips, therefore, should enable us to differentiate between hereditary variations and environmental variations. While hereditary variations are transmitted from generation to generation, environmental variations are temporary and have nothing to do with the last or the next generation.

As outlined above, hereditary variations within a progeny result due to sexual reproduction. If there were no sexual reproduction, there could be no hereditary variation except those due to mutations among the individuals of the same progeny. It is due to this reason that in asexually reproducing plants, the population appears fairly uniform. Obviously sexual reproduction has played a very important role in evolution. A brief account of sexuality in animals and plants has, therefore, been included here.