A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a polypeptide or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism's cells and pass genetic traits to offspring. All organisms have many genes corresponding to various biological traits, some of which are immediately visible, such as eye colour or number of limbs, and some of which are not, such as blood type, increased risk for specific diseases, or the thousands of basic biochemical processes that comprise life. The vast majority of living organisms encode their genes in long strands of DNA. The present publication is an extensive work on gene evolution and covers much more of the subject as is generally expected by the students going up for the examinations of several universities in India and abroad. This book presents a logical and practical approach to the various complexities and intricacies of the subject at length.