We are entering a new era of increasing understanding of how genetics influences human health and development, agricultural productivity and the ecological balance of the planet. This will be crucial to decisions involving personal, medical, societal, economic and environmental issues. This book aims to convey to non-specialists the excitement and significance of recent discoveries dealing with genes and the innovative capabilities that stem from these advances. Introductory chapters trace the historical path to present views about inheritance, introducing the concept of the gene, how genes are passed from one generation to the next, how they determine traits in all living organisms, and how alteration in genes influence traits and cause disease. Some basic chemistry is introduced at this stage to enable the reader to understand that modern genetics is a molecular science. Subsequent chapters describe how genes are encoded in the molecular structure of DNA and how that information is decided to create a functional organism. An important feature of that process - the intricate "switches" that turn genes on and off in the proper tissues at proper times - is emphasized because of its critical role in guiding normal growth and development. All of this is a prelude to chapters that describe how mutations - spontaneous, induced or directed - alter normal genetic functions to produce diseases such as heart and mental diseases, cancer and colour blindness. These chapters further describe current efforts to map all human genes and how all this information is being used to find genes, and to analyze their status as a means to improving the diagnosis, prevention, and cure of genetic disorders. Similar efforts and technology are being applied for the improvement of agriculturally important crops and animals, new industrial products, and a new apprieciation of the natural world and its origins.