This new edition builds on the success of the first by reviewing the increased understanding of the mechanisms of gene action in humans, focusing particularly on those derived from the study of genetic diseases. It deals mainly with the fundamental aspects of gene arrangement and expression rather than mutation. As well as updating and revising material from the first edition, it covers methods of exploring gene function and contains a range of chapters on specific systems which raise issues of special interest such as imprinting or homologous genes within clusters.