It has been hypothesized that Native Americans arrived from Asia in three separate migrations: the Paleo-Indians which occupy South, Central and North America; the Na-Dene of northwestern Canada and Alaska; and the Eskimos and Aleuts of the Arctic. To test this hypothesis, we are analyzing the mitochondrial DNA (mtDNA) sequence variation of Amerindians, Asians and Siberians by polymerase chain reaction amplification, digestion with multiple restriction endonucleases and D-loop sequencing. The mtDNA variation of the populations is then compared by phylogenetic analysis and by calculation of genetic distances (D[xy]) and population substructures (GST). These studies have revealed that Paleo-Indians harbor four mtDNA lineages (haplotype clusters A-D) which arrived in the Americas between 23,000 and 46,000 years before present (YBP) in one or two migrations. The Na-Dene represent a subsequent migration baring one mtDNA lineage (Cluster A*) which arrived about 6,000 to 12,000 (YBP). We propose to extend our mtDNA studies to (1) determine if there were two Paleo-Indian migrations, (2) confirm the homogeneity of the Na-Dene migration, (3) determine if there was a distinct Eskimo-Aleut migration, (4) search for the Asian or Siberian progenitors of the Amerindian migrations and (5) refine our estimates of the migration times. To test for two Paleo-Indian migrations, 23 Paleo-Indian tribes from North, Central and South America will be screened for a non-uniform distribution of haplotype clusters A-D and to confirm preliminary data that haplotype cluster B is younger than the others. The homogeneity of the Na-Dene migration will be confirmed by showing that additional Alaskan and Canadian Na-Dene mtDNAs belong to the haplotype cluster A* and are of same age. The relationship of the Eskimos and Aleuts to the Paleo-Indians and Na-Dene will be examined by collecting Eskimo and Aleut samples throughout the arctic and determining their mtDNA haplotypes and sequence variation. The origins of Amerindians will be sought by screening 12 Asian and Siberian populations for the mtDNA variants known to be associated with each Amerindian migration and analysis of Asian-Siberian and Amerindian sequence homologies. The age of the migrations will be refined by subtracting