Her subtitle’s bold claim notwithstanding, Nicolson does maintain a steady balance between breadth and depth in this primer on genetic mechanisms and issues. In a text split into easily digestible blocks, she covers genetic traits, DNA, mutation, the work of the Human Genome Project and other research, the medical possibilities of cloning, and its potential hazards, while Cowles keeps the tone light with playful, sometimes silly cartoon illustrations. Sidebars offer instructions for very basic demonstrations of each topic. Though she doesn’t quite get to everything—Crick and Watson, yes; their little-known collaborator Rosalind Franklin, no, for instance—she does give readers the big picture, from the common genetic inheritance of all living things to how DNA evidence helped to nail the Unabomber. In addition, she expertly sets the stage for upcoming developments in the already-begun genetic revolution. (index, glossary) (Nonfiction. 7-10)