The tools of molecular biology have revolutionised our understanding of gene structure and function and changed the teaching of genetics in a fundamental way. The transition from classical genetics to molecular genetics was initiated by two discoveries. One was the discovery that DNA has a complementary double helix structure and the other that a universal genetic code does exist. Both led to the acceptance of the central dogma that RNA molecules are made on DNA templates. The last twenty years have seen remarkable growth in our knowledge of molecular genetics, most of which is the outcome of recombinant DNA technology. This technology which is not limited to cloning, sequencing, and expression has created a biotechnology industry of its own, the purpose of which is to develop new diagnostic and therapeutic approaches in medicine. Both industries in collaboration with the biomedical community are now engaged in laying down the foundation of molecular medicine. The present volume seeks to provide a coherent account of the new science of molecular genetics. Its content however is by no means exhaustive, partly because of the publication explosion but more because of space restrictions. A rudimentary knowledge of genetics on the reader's part is assumed. Quite understandably, considerable emphasis is placed on major technical advances but not without expounding numerous new ideas and phenomena including alternative splicing, POR, DNA methylation, genomic imprinting, and so on.