Haplogroup O3 (Y-DNA)
In human genetics, Haplogroup O3 (M122) is a Y-chromosome haplogroup.
Haplogroup O3 is a descendant haplogroup of haplogroup O.  Some researchers believe that it first appeared in China approximately 10,000 years ago.  However, others believe that the high internal diversity of Haplogroup O3 indicates a late Pleistocene (Upper Paleolithic) origin in South China or Southeast Asia of the M122 mutation that defines the entire O3 clade, while the common presence among a wide variety of modern East and Southeast Asian nations of closely related haplotypes belonging to certain subclades of Haplogroup O3 is considered to point to a recent (e.g., Holocene) geographic dispersion of a certain subset of the ancient variation within Haplogroup O3.  The spread of these particular subsets of Haplogroup O3 is conjectured to be closely associated with the sudden agricultural boom associated with rice farming.
Although Haplogroup O3 appears to be primarily associated with Chinese populations, it also forms a significant component of the Y-chromosome diversity of most modern populations of the East Asian region. Haplogroup O3 is found in over 50% of all modern Chinese males (ranging up to over 80% in certain regional subgroups of the Han ethnicity), about 40% of Manchurian, Korean, and Vietnamese males, about 35% of Filipino and Malaysian males, about 25% of Zhuang males, and about 15% to 20% of Japanese males. The distribution of Haplogroup O3 stretches far into Central Asia (approx. 18% of Khalkh Mongols and approx. 6.2% of Altayans) and Oceania (approx. 25% of Polynesians), albeit with reduced frequencies of most subclades. It should be noted that Haplogroup O3- Y-chromosomes, which are not defined by any identified downstream markers, are actually more common among certain non-Chinese populations than among Chinese ones, and the presence of these O3- Y-chromosomes among various populations of Central Asia, East Asia, and Oceania is more likely to reflect a very ancient shared ancestry of these populations rather than the result of any historical events. It remains to be seen whether Haplogroup O3- Y-chromosomes can be parsed into distinct subclades that display significant geographical or ethnic correlations.
Among all the populations of East and Southeast Asia, Haplogroup O3 is most closely associated with those that speak a Sinitic, Tibeto-Burman, or Hmong-Mien language. Haplogroup O3 comprises about 50% or more of the total Y-chromosome variation among the populations of each of these language families. The Sinitic and Tibeto-Burman language families are generally believed to be derived from a common Sino-Tibetan protolanguage, and most linguists place the homeland of the Sino-Tibetan language family somewhere in northern China. The Hmong-Mien languages and cultures, for various archaeological and ethnohistorical reasons, are also generally believed to have derived from a source somewhere north of their current distribution, perhaps in northern or central China. The Tibetans, however, despite the fact that they speak a language of the Tibeto-Burman language family, have a very high percentage of the otherwise rare Haplogroup D1, which is also found at much lower frequencies throughout Central and Northeast Asia. These facts suggest that Haplogroup O3 is characteristic of the easterly part of the zone of transition between the Northeast Asian and Southeast Asian genepools: namely, the region that comprises the North China Plain and the area between the Yellow and Yangtze rivers. It is notable that Haplogroup O3 is the only haplogroup that occurs at high frequencies among populations that possess Northeast Asian genetic characteristics as well as among populations that possess Southeast Asian genetic characteristics.
Haplogroup O3 has been implicated as a diagnostic genetic marker of the Austronesian expansion when it is found in populations of Oceania. Its distribution in Oceania is mostly limited to the traditionally Austronesian culture zones, including moderately high frequencies in the Philippines, Malaysia, Indonesia, and Polynesia, with generally lower frequencies found in coastal and island Melanesia, Micronesia, and Taiwanese aboriginal tribes.
The subgroup O3a5-M134 is particularly closely associated with Sino-Tibetan populations, and it is generally not found outside of areas where a Sino-Tibetan language is currently spoken or that are historically supposed to have suffered Chinese colonization or immigration, such as Korea, Japan, Vietnam, Malaysia, the Philippines, and Indonesia. However, its presence among non-Sino-Tibetan populations is always very limited and never amounts to more than 10% of the total Y-chromosome diversity. There are also reports that Y-chromosomes belonging to Haplogroup O3a5 have been sampled from populations of such far-flung places as Western Samoa. Surprisingly, Haplogroup O3a5-M134 Y-chromosomes have also been found in about 1% to 3% of indigenous Australian men in the northwest of that continent, which might indicate that a certain degree of contact has occurred between the Austronesian expansion from Asia and some indigenous Australian populations. The fact that Haplogroup O3a5 is so strongly associated with Chinese populations, however, and the fact that no Y-chromosome haplogroups characteristic of Austronesian populations have been found among these indigenous Australian populations may be taken to suggest the possibility of some direct Chinese-Australian contact in the precolonial era.
Haplogroup O3's brother clade, Haplogroup O1, displays a similar geographical distribution, being found among nearly all the populations of East and Southeast Asia, but generally at a frequency much lower than that of Haplogroup O3. Another brother clade, Haplogroup O2, has an impressive extent of dispersal, as it is found among the males of populations as widely separated as the Mundas of India and the Japanese of Japan; however, Haplogroup O2's distribution is much more patchy, and the Haplogroup O2 Y-chromosomes found among the Mundas and the Japanese belong to distinct subclades.