Big science has come to biomedicine in the form of the Human Genome Project: a megabuck, multisite effort to map and sequence all three billion base pairs that constitute the human genetic program. But it's not come without controversy. Scientists have deplored the cost (and drain on other research), as well as the tedious nature of the effort, and have raised issues of coordination, competition, and ethics. Here, science writer Wingerson (Discover, Science Digest, etc.) takes on the politics and the personalities in an eyewitness-account of science in progress. Essentially, Wingerson makes the case for the Genome Project through observations of the scientists studying families affected by severe hereditary disease. The hope has always been to find a genetic marker--a bit of DNA so close to the defective gene that it is always inherited with it. In contrast, family members who do not get the disease inherit a different form of DNA at the same marker site. The forms are called polymorphisms, and the advent of biotechnology provides ways to cut up and sort fragments of DNA in search of such markers. (Put simply, it would be as if blue-eyed family members inherited the defective gene but brown-eyes didn't.) The breakthrough came when researchers studing a large family in Venezuela found a marker for Huntington's disease on chromosome 4. That inspired geneticists to study Amish, Mennonite, Mormon, and other large kindreds for clues to such disorders as manic-depressive illness, Tourette's syndrome, and cystic fibrosis. Wingerson follows the teams to the communities where bloods are drawn and interviews conducted. She writes compassionately about the scientists as well as those afflicted--an approach particularly effective in her description of the work of a woman studying manic-depressive illness among the Amish. Elsewhere, she does her best to make the laboratory procedures comprehensible (but they still sound boring) and come to grips with the ethical issues. A good beginning to a tale that may be the medical story of the 21st century.