Earlier studies have shown the Ainu to have substantial amounts of mitochondrial chromosome Y haplogroup, believed to be related to the establishment of the Okhotsk culture in Hokkaido, and one of the ancestral lineages of the Ainu. The paper excerpts below help pinpoint the possible source of geneflow into the Hokkaido Ainu of haplogroup Y.
Theodore G. Schurr, et al. Mitochondrial DNA variation in Koryaks and Itel’men: population replacement in the Okhotsk Sea-Bering Sea region during the Neolithic. American journal of physical anthropology 1999
In this study, we analyzed the mitochondrial DNA (mtDNA) variation in 202 individuals representing one Itel’men and three Koryak populations from different parts of the Kamchatka peninsula….. Together, the Koryaks and Itel’men were found to have mtDNAs belonging to three (A, C, and D) of the four major haplotype groups (haplogroups) observed in Siberian and Native American populations (A-D). In addition, they exhibited mtDNAs belonging to haplogroups G, Y, and Z, which were formerly called “Other” mtDNAs. While Kamchatka harbored the highest frequencies of haplogroup G mtDNAs, which were widely distributed in eastern Siberian and adjacent east Asian populations, the distribution of haplogroup Y was restricted within a relatively small area and pointed to the lower Amur River-Sakhalin Island region as its place of origin. In contrast, the pattern of distribution and the origin of haplogroup Z mtDNAs remained unclear. Furthermore, phylogenetic and statistical analyses showed that Koryaks and Itel’men had stronger genetic affinities with eastern Siberian/east Asian populations than to those of the north Pacific Rim. These results were consistent with colonization events associated with the relatively recent immigration to Kamchatka of new tribes from the Siberian mainland region, although remnants of ancient Beringian populations were still evident in the Koryak and Itel’men gene pools.
…These analyses showed that the mtDNAs observed in contemporary New World populations were a subset of Asian haplotypes which consisted of primarily four mtDNA lineages, or haplogroups, designated A, B, C, and D. Within these mtDNA lineages, only a small number of haplotypes were found to be shared between Asian and Native American populations, suggesting that a limited number of founders gave rise to ancestral Native American populations. The sequence divergence values for the haplogroups present in Native Americans further indicated that ancestral populations bringing at least haplogroups A, C, and D arrived early in the New World, around 35,000–25,000 years before present (YBP), and that haplogroup B might represent a second, later migration which contributed mtDNAs to the genetic stock of Amerindians (Torroni et al., 1992, 1993a, 1994a).