This second edition has been extensively revised, rewritten, updated, and expanded. A new section on genomics (Part II) has been added. Twenty new plates deal with a variety of topics such as the molecular bases of genetics, regulation and expression of genes, genomic imprinting, mutations, chromosomes, genes predisposing to cancer, ion channel diseases, hearing and deafness, a brief guide to genetic diagnosis, human evolution, and many others. The Chronology of Important Advances in Genetics and the Definitions of Genetic Terms have been updated. As in the first edition, references are included for further reading. Here and in the list of general references, the reader will find access to more detailed information than can be presented in the limited space available. Websites for further information are included.