The basic principles of genetics were laid down by Mendel and Galton towards the close of 19th century. But it is only during the past few years the science of genetics including human genetics has made rapid progress. The discovery of the biological role of nucleic acid, the uncovering of the structure of genetic information and its role in regulating life processes and discoveries, the importance of which can hardly be over estimated, with increasing control of communicable diseases and infant moratality, abnormalities are assuming a proportionately greater importance in medical practice. Over 2300 hereditary diseases have been identified and more are added to the list every year. According to many authors, genetically conditioned disease with a clear genetic component account for 25-40 percent of all cases treated by the health services.[44]
Human genetics is much more than the study of mere hereditary diseases and inborn abnormalities. It has emerged as a basic biological science for understanding the endogenous factors in health and disease and the complex intraction between nature and nurture. Owing to rapid specialization, several branches in genetics have come into being e.g. cytogenetics, biochemical genetics, clinical genetics, pharmacogenetics, immunogenetics, microbial genetics, population genetics and so on. Achievements in these fields have created a basis for effective medical and preventive intervention in many diseases, and also possibly of "Genetic Engineering" i.e. of controlling the traits of an individual.