Haplogroup O2 (Y-DNA)
In human genetics, Haplogroup O2 (P31, M268) is a Y-chromosome DNA haplogroup.
Haplogroup O2 is a descendent branch of the greater Haplogroup O.
Although Haplogroup O2 is not found so frequently in modern human populations as its brother clade, Haplogroup O3, it is notable for the peculiarities of its geographical distribution. Like all clades of Haplogroup O, Haplogroup O2 is found only among the males of modern Eastern Eurasian populations. However, unlike Haplogroup O3, which is shared in common by almost all populations of Eastern Eurasia as well as many populations of Oceania, Haplogroup O2 is generally found only among certain "fringe" populations, such as the Austroasiatic tribes of India and Bangladesh, the Nicobarese of the Nicobar Islands in the Indian Ocean, and the Koreans, Japanese, and Tungusic peoples of Northeast Asia.
Besides its widespread and patchy distribution, Haplogroup O2 is also notable for the fact that it can be divided into two major subclades that show almost completely disjoint distribution. One of these subclades, Haplogroup O2a (M95), is found among some (mostly tribal) populations of South and Southeast Asia, as well as among the Khmers of Cambodia and the Balinese of Indonesia. There are also some reports that Haplogroup O2a may be associated with the so-called Negrito populations of mainland Southeast Asia, such as the Semang and the Senoi, but it is not clear whether this is their original Y-chromosome heritage or rather the result of incursion of Austroasiatic Y-chromosomes from the Khmers and related peoples who may have lent the Negritos their Austroasiatic languages in a manner similar to the Bantus' hypothesized lending of their languages and Haplogroup E Y-chromosomes to the pygmoid peoples of Africa, such as the Baka and Mbuti. The other major subclade, Haplogroup O2b (SRY465, M176), is found almost exclusively among the Koreans, the Japanese, and the Manchus.
The Northeast Asian Haplogroup O2b suggests a very interesting sort of relationship between the Tungusic, Korean, and Japanese peoples. Haplogroup O2b's parent haplogroup, Haplogroup O2*, appears to have been thinly spread throughout East Asia since prehistoric times. The derived Haplogroup O2b* (M176) is found at low frequency across the populations of the whole of Greater Manchuria, including the Tungusic, Korean, Japanese, and even the Daur people, who speak a Mongolic language that has traditionally been considered to have derived from an ancient dialect transitional between the Proto-Mongolic and Proto-Tungusic languages. One major subbranch, O2b1* (P49), is shared between the Korean and Japanese populations (with a significantly higher STR diversity among the Koreans), but its distribution does not reach the Tungusic or Daur peoples to the north. Finally, the most derived subbranch, Haplogroup O2b1a (47z), is essentially restricted to the Japanese population, although it has sporadically been detected in a few individuals who reside within the extent of the erstwhile Great Japanese Empire, in which cases it is believed to represent minor admixture from male Japanese soldiers or civilians into the local populations within the last several generations; patrilineal descent from a Japanese visitor or immigrant to some of these lands during earlier historical times is another possibility. This "nested" hierarchical and region-specific distributional pattern tends to suggest the following sequence of events:
1) The M176 mutation that defines the O2b Y-chromosome lineage first arises on an ancestral O2* chromosome belonging to a man who already resides within Greater Manchuria, or who at least already belongs to a specific "proto-Tungus-Korean" tribe.
2) Sometime after the proto-Koreans have branched off from the other populations of the Greater Manchurian region, the P49 mutation that defines Haplogroup O2b1* arises in a proto-Korean male, whose lineage becomes very successful and increases in number among the prehistoric proto-Korean population.
3) One regional subgroup of the proto-Koreans distinguishes itself from the others either culturally or by physically migrating away from their proto-Korean brethren. After the split from the greater proto-Korean population is complete, the 47z mutation that defines Haplogroup O2b1a occurs in a male of this now proto-Japanese population, who produces many male descendants and increases the frequency of the O2b1a lineage among the proto-Japanese. This very specific Haplogroup O2b1a lineage now occupies about 42.5% of the total of Haplogroup O lineages, or about 22.0% of all Y-chromosomes, among the modern Japanese, which probably reflects extreme hegemony of a certain close-knit clan in the history of the Japanese people.
In addition to suggesting a phylogenetic relationship between at least a subset of the ancestors of the Tungusic, Korean, and Japanese peoples, the distribution of Haplogroup O2b and its subbranches also argues strongly against any significant intermingling of any of these peoples during historical times.
The other major Northeast Asian Y-chromosome haplogroup, Haplogroup C3, is also found among the Tungusic, Korean, and Japanese peoples, as well as among the Mongolian peoples, Turkic peoples, and even the Ainu of Japan and the Na-Dené peoples of North America, but Haplogroup C3 displays a cline of frequency opposite to that of Haplogroup O2, to the effect that Haplogroup C3 is more frequent among the more northerly populations (Mongolian, Turkic, Northern Tungusic, Koryak, Nivkh, etc.), whereas Haplogroup O2 is more frequent among the more southerly populations (Southern Tungusic, Korean, and Japanese), and it is entirely absent from the Ainu and Na-Dené populations. The typically Sino-Tibetan and Southeast Asian Haplogroup O3 is also shared in common by most Tungusic, Mongolic, Turkic, Korean, and Japanese populations with various frequency and diversity values, which may be a genetic trace of a demic diffusion of Neolithic culture from China; however, the common occurrence at a low frequency throughout Northeast Asia of Y-chromosome Haplogroup D1 and several mtDNA haplogroups that are typical of Tibetans in addition to the Sino-Tibetan-Austronesian Haplogroup O3 may reflect some sort of relationship between the peoples of Northeast Asia and the peoples of Tibet rather than a major Neolithic or even more recent influence from China.