University of Agricultural Sciences, Bangalore

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Includes bibliographical references.

Genetics has now assumed la central role in biology, as an understanding of gene structure and expression is important in the study of cell biology, biochemistry, microbiology and biotechnology. The historical development of genetics is conventionally divided into four phases. The first is the classical phase of Mendelian or transmission genetics which deals with the transmission of genes from generation to generation as deduced by the observation of differing traits or phenotypes, and genetic recombination. The second phase, cytogenetics, deals with the correlation of genetic and cytological (Especially chromosomal) features of particular genetic systems. The third phase, biochemical genetics, deals with the chemical nature and action of heredity determinants. The fourth phase, molecular genetics, is concerned with the interpretation of genetic mechanisms at the molecular level in terms of the principles of chemistry and physics. Running parallel with these phases were studies on population genetics and quantitative genetics which deals with variation of genes within populations. Modern genetics is a combination of two or more of the above areas.