Different genes in an organism are meant for the synthesis of different proteins. The hereditary nature if every living organism is defined by its genome, which consists of a long sequence of nucleic acid that provides the information needed to construct the organism. By a complex series of interactions, the sequence of individual subunits of nucleic acid determines hereditary features. The genome contains the complete set of hereditary information for any organism. Each gene is sequence within nucleic acid that represents a single protein. Each of discrete nucleic acid molecules comprising the genome may contain a large number of genes. The concept of the gene as a continuous stretch of DNA had been shattered with the discovery of the introns, but alternative splicing and genes-within-genes were yet to be revealed. Identification of cellular oncogenes seemed to promise an understanding of cancer, but the mechanism of their action –and the existence of tumor suppressor genes-still subjects for speculation. The topics that are covered and the approach I had taken to describe them make this book suitable for undergraduate and post graduate students in molecular biology and biotechnology courses.