Genetics is the branch of biological science which deals with the transmission of hereditary factors from one generation to the other and also the ways in which they express themselves during the development and life of an individual. It is the science of inheritance. It is concerned with the laws of storage, transmission and realization of information for development and function of living organisms. Human genetics is based on general principles derived originally from the study of plants and animals. These principles are valid for man as they are for other organisms. Since other organism are better adapted to experimental work these general principles can be demonstrated more clearly in such organisms. Therefore while analyzing human inheritance such references are always helpful.