WHILE MUCH OF the promise of the revolution in genetic knowledge lies in the future—when scientists hope to produce dramatic cures through genetic engineering—one thing the revolution has already produced in abundance is information. These days, scientists uncover a new human gene nearly every week. They have developed blood tests that can tell people whether they are carriers of disease-related genetic mutations. Among these are tests that detect the genetic mutations associated with Alzheimer's disease, some types of breast and ovarian cancer, cystic fibrosis, Duchenne's muscular dystrophy, fragile X syndrome, Huntington's disease, sickle-cell anemia, and some forms of hemophilia. In 1999, U.S. laboratories performed 4 million genetic tests.

These new tests for prying personal medical information out of an individual's genes are only the latest additions to an already well stocked toolbox of...