ASIAN AFFINITIES AND CONTINENTAL RADIATION OF THE 4 FOUNDING NATIVE-AMERICAN MTDNAS

The mtDNA variation of 321 individuals from 17 Native American populat ions was examined by high-resolution restriction endonuclease analysis . All mtDNAs were amplified from a variety of sources by using PCR. Th e mtDNA of a subset of 38 of these individuals was also analyzed by D- loop sequencing. The resulting data were combined with previous mtDNA data from five other Native American tribes, as well as with data from a variety of Asian populations, and were used to deduce the phylogene tic relationships between mtDNAs and to estimate sequence divergences. This analysis revealed the presence of four haplotype groups (haplogr oups A, B, C, and D) in the Amerind, but only one haplogroup (A) in th e Na-Dene, and confirmed the independent origins of the Amerinds and t he Na-Dene. Further, each haplogroup appeared to have been founded by a single mtDNA haplotype, a result which is consistent with a hypothes ized founder effect. Most of the variation within haplogroups was trib al specific, that is, it occurred as tribal private polymorphisms. The se observations suggest that the process of tribalization began early in the history of the Amerinds, with relatively little intertribal gen etic exchange occurring subsequently. The sequencing of 341 nucleotide s in the mtDNA D-loop revealed that the D-loop sequence variation corr elated strongly with the four haplogroups defined by restriction analy sis, and it indicated that the D-loop variation, like the haplotype va riation, arose predominantly after the migration of the ancestral Amer inds across the Bering land bridge.