Substantially revised to reflect the changes in this rapidly developing field, this edition (the first edition came out in 1999) features 64 new essays, heavy revision of 131, and omission of 26, and new or updated bibliographies for all entries. Two new appendices have been added , on web sites and Nobel prizes. Among the topics included are altruism, ancient DNA, antibodies, bioethics, biological determinism, cancer, cell culture of plants and animals, diabetes, epistasis, eugenics, genetically modified foods, and pseudogenes. Several entries are devoted to case studies of model organisms, and there are multiple entries on aspects of DNA, gene regulation, gene therapy, genetic code, genetic engineering, and chromosomes. The contributors are academics, researchers, and independent scholars in the US.