Haplogroup O2b (Y-DNA)

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Haplogroup O2b (SRY465, a.k.a. M176) is a human Y-chromosome DNA haplogroup. It is a descendant haplogroup of Haplogroup O2. Haplogroup O2b is found mainly in the northeastern parts of East Asia, from the Daur people of Inner Mongolia to the Japanese of Japan; however, haplogroup O2b has also been found at significant frequency among some populations of Southeast Asia, including those of Indonesia, Thailand, and Vietnam.^[1] This haplogroup is found with its highest frequency and diversity values among modern populations of Japan and Korea and is absent from most populations in China.^{[citation needed]}

[edit] Subgroups

The phylogeography of Haplogroup O2b suggests a very ancient origin in Manchuria, followed by a long period of isolated evolution and population increase within the Korean Peninsula. Only the most ancient branches of this haplogroup, which are labeled as Haplogroup O2b*, have been detected among the indigenous populations of Inner Mongolia and Manchuria, and even then they are found only at very low frequencies. Haplogroup O2b* Y-chromosomes have been detected at a similarly low frequency among the Koreans, but Korean males display a very high frequency of a derived subclade, Haplogroup O2b1* (P49). In fact, Haplogroup O2b1* comes close to being the modal Y-chromosome haplogroup in Korea, occurring in approximately 30% of all Korean males.

A subclade of Haplogroup O2b1, namely Haplogroup O2b1a (47z), is found at a fairly high frequency among the Yamato people and Ryukyuan populations of Japan. Haplogroup O2b1a has been detected in approximately 22% of all males who speak a Japonic language, while it has not been found at all among the Ainu or Nivkhs of the northern extremes of the Japanese Archipelago. Based on the STR haplotype diversity within Haplogroup O2b1a, it has been estimated that this haplogroup began to experience a population expansion among the proto-Japanese of approximately 4,000 years ago, which makes it a good candidate for a marker of the intrusion of a Neolithic population of the prehistoric Korean Peninsula into the southwestern parts of the Japanese Archipelago. However, the parent haplogroup, O2b1*, is also found among Japanese, although at a relatively low frequency of approximately 4% to 7%, and the descendant haplogroup O2b1a is either completely absent from or found at only extremely low frequency (which could represent historical Japanese admixture) among samples of modern Koreans, which suggests the possibility that Haplogroup O2b1* might have colonized the Japanese Archipelago much earlier, with the subgroup O2b1a subsequently evolving within the proto-Japanese-Ryukyuan population of the western parts of the archipelago.