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. When proteins are manufactured, the gene is first copied into RNA as an intermediate product. In other cases, the RNA molecules are the actual functional products. Some viruses store their entire genomes in the form of RNA, and contain no DNA at all. The overarching theme of the book, the important link between genes, is mirrored in the text. Efforts have been made to present the principles of gene manipulation and its associated techniques, in sufficient detail to enable non-specialist reader to understand them. This book will prove useful to students, teachers and researchers.