 Throughout the 1980s and 1990s, teams of researchers in the ever-expanding pool of medical genetics and human genetics programs competed to be the first to find the precise genomic location of disease-causing genes. The challenge was to determine which chromosome, then which stretch of DNA, and finally which specific nucleic acid mutation was responsible for conditions like cystic fibrosis and breast cancer; the leaders of the teams that crossed the finish line first became scientific celebrities. The excitement surrounding the genetic discoveries was partly about the thrill of a scientific race; but more than that, it was also about the promise of genetic tests that could tell patients more accurately whether or not they were likely to develop some devastating disease and, beyond that, lead to the development of gene-based treatments or even cures for those diseases.