The first published map of human genetic differences offers a major step toward truly personalized medicine, from predicting who will get what disease to finding ways of choosing the best drug for an individual patient, scientists said. The map, published on Thursday, looks at more than 1.5 million tiny genetic differences among 71 people, said the team at Perlegen Sciences, Inc., a spinoff of Mountain View, California-based gene chip maker Affymetrix. This is enough to find some of the most common genetic variations involved in disease, said David Cox, Perlegen's chief scientific officer.