The Y chromosomes of 549 individuals from Siberia and the Americas were analyzed for 12 biallelic markers, which defined 15 haplogroups. The addition of four microsatellite markers increased the number of haplotypes to 111. The major Native American founding lineage, haplogroup M3, accounted for 66% of male Y chromosomes and was defined by the biallelic markers M89, M9, M45, and M3. The founder haplotype also harbored the microsatellite alleles DYS19 (10 repeats), DYS388 (11 repeats), DYS390 (11 repeats), and DYS391 (10 repeats). In Siberia, the M3 haplogroup was confined to the Chukotka peninsula, adjacent to Alaska. The second major group of Native American Y chromosomes, haplogroup M45, accounted for about one-quarter of male lineages. M45 was subdivided by the biallelic marker M173 and by the four microsatellite loci alleles into two major subdivisions: M45a, which is found throughout the Americas, and M45b, which incorporates the M173 variant and is concentrated in North and Central America. In Siberia, M45a haplotypes, including the direct ancestor of haplogroup M3, are concentrated in Middle Siberia, whereas M45b haplotypes are found in the Lower Amur River and Sea of Okhotsk regions of eastern Siberia. Among the remaining 5% of Native American Y chromosomes is haplogroup RPS4Y-T, found in North America. In Siberia, this haplogroup, along with haplogroup M45b, is concentrated in the Lower Amur River/Sea of Okhotsk region. These data suggest that Native American male lineages were derived from two major Siberian migrations. The first migration originated in southern Middle Siberia with the founding haplotype M45a (10-11-11-10). In Beringia, this gave rise to the predominant Native American lineage, M3 (10-11-11-10), which crossed into the New World. A later migration came from the Lower Amur/Sea of Okhkotsk region, bringing haplogroup RPS4Y-T and subhaplogroup M45b, with its associated M173 variant. This migration event contributed to the modern genetic pool of the Na-Dene and Amerinds of North and Central America.

We have initiated a study of ancient male migrations from Siberia to the Americas using Y chromosome polymorphisms. The first polymorphism examined, a C→T transition at nucleotide position 181 of the DYS199 locus, was previously reported only in Native American populations. To investigate the origin of this DYS199 polymorphism, we screened Y chromosomes from a number of Siberian, Asian, and Native American populations for this and other markers. This survey detected the T allele in all five Native American populations studied at an average frequency of 61%, and in two of nine native Siberian populations, the Siberian Eskimo (21%) and the Chukchi (17%). This finding suggested that the DYS199 T allele may have originated in Beringia and was then spread throughout the New World by the founding populations of the major subgroups of modern Native Americans. We further characterized Native American Y chromosome variation by analyzing two additional Y chromo-some polymorphisms, the DYS287 Y Alu polymorphic (YAP) element insertion and a YAP-associated A→G transition at DYS271, both commonly found in Africans. We found neither African allele associated with the DYS199 T allele in any of the Native American or native Siberian populations. However, we did find DYS287 YAP+ individuals who harbored the DYS199 C allele in one Native American population, the Mixe, and in one Asian group, the Tibetans. A correlation of these Y chromosome alleles in Native Americans with those of the DYS1 locus, as detected by the p49a/p49f (p49a,f) probes on TaqI-digested genomic DNA, revealed a complete association of DYS1 alleles (p49a,f haplotypes) 13, 18, 66, 67 and 69 with the DYS199 T allele, while DYS1 alleles 8 and 63 were associated with both the DYS199 C and T allele.

It is generally accepted that the earliest human occupants of Europe arrived during the Paleolithic, on the order of 40,000-50,000 years before the present (YBP), and that agriculture arose in the Near East during the Neolithic, ∼10,000 YBP. However, debate has arisen over the mechanism of dispersal of farming within Europe. The demic-diffusion model proposed by Ammerman and Cavalli-Sforza (1984) postulates that extensive migrations of Near Eastern farmers during the Neolithic brought agricultural techniques to the European continent. Under this model, the migrant farming populations expanded with little admixture with the Mesolithic European inhabitants, so that a large proportion of the present-day European gene pool should be derived from the Neolithic migrants. In contrast, others have proposed a cultural-diffusion model (Dennell 1983) in which the transfer of agricultural technology occurred without significant population movement. Under this model, the majority of the genetic diversity within Europe would have its roots in the Paleolithic. Genetic evidence in support of the demic-diffusion model initially came from analyses of classic gene-frequency data (Menozzi et al. 1978; Cavalli-Sforza et al. 1994; Piazza et al. 1995). In these studies, synthetic genetic maps of Europe and the Near East were constructed with the use of principal-components analysis to condense the information from numerous loci. In general, it was observed that the first principal component summarized one-quarter to one-third of the total variation and that it appeared to support a clinal pattern of geographic distribution resembling the archaeological map of the spread of early farming. A later study of seven hypervariable nuclear DNA markers offered similar interpretations of a northward and westward

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