Over 100 of the major illustrations are completely new or significantly revised to increase clarity.

Includes dramatic new results on the evolutionary relationships in the tree of life (Chapter 1).

Includes a new discussion of the organization of chromatin in the nucleus of nondividing cells into chromosome territories, and of how these might contribute to genetic regulation (Chapter 3). The DNA sequence organization of human centromeres has also been included based on new data from the Human Genome Project.

Contains an updated model for homologous recombination (Chapter 4). This model recognizes that recombination is initiated by a double-stranded break and that the process includes two Holliday junctions. The authors also distinguish between the noncrossover pathway for break repair and the crossover pathway.

Chapter 5 features a major new section on tracing human history through Y-chromosome haplotypes. This section gives several examples, in detail, and also includes new data on the effects of chemicals in the environment on nondisjunction.

DNA synthesis makeover (Chapter 6) in light of new findings that the mechanism of primer removal and replacement is rather different in eukaryotes than it is in prokaryotes.

New discussions on transcription and RNA processing as coupled processes, in which each step in the process recruits the proteins needed to accomplish the next step along the way. Also includes a new section on protein folding, which emphasizes the role of trigger factor, chaperones, and chaperonins in helping large or slowly folding polypeptides to find their correct three-dimensional structure.

Hardly any field of genetics and genomics moves as rapidly as that of gene regulation. Regulation by means of RNA has become a particularly active field. This new edition includes major new discussions of riboswitches, small regulatory RNAs that control translation ("kissing complexes"), and the mechanism of RNA interference (RNAi).

Completely reorganized and expanded chapter on genomics, proteomics, and genetic engineering (Chapter 10).

The fourth edition contains a major new section on genetic control of the cell cycle through cyclins, cyclin-dependent protein kinases, and other mechanisms, such as proteolysis.

Chapter 14 features a major new section on molecular evolution that focuses on how inferences about gene evolution, protein evolution, and organismic evolution can be gleaned from DNA or protein sequences.

Contains a thoroughly updated section on the polymorphism in the serotonin reuptake transporter and its relation to risk of severe depression in response to stressful life events.

In addition to the variety of updated end-of-chapter problems, the authors have added a new type of problem to each chapter to help students learn the proper use of key genetics terms in context.