Genetic researchers at Utah-based Sorenson Molecular Genealogy Foundation and Italy's University of Pavia have discovered that 95 percent of American Indians descend from six ancestral mothers who crossed Asia to the Americas 20,000 years ago, United Press International reports. According to a release, this marks the first time all known American Indian mitochondrial DNA (mtDNA) sequences and lineages have been compiled, corrected and organized into a single tree with branches dated. The study, which was published online by the Public Library of Science, identifies the six surviving Native American mtDNA lineages that are dated to approximately 20,000 years ago, designated as A2, B2, C1b, C1c, C1d and D1. The study also confirms the presence of five geographically limited genetic groups: X2a, D2, D3, C4c and D4h3. The lead study author notes that the five more rare genetic groups will help researchers isolate branches within the pan-American groups and make conclusions about different migratory events (UPI, 3/15/08).