In genetics,
Haplogroup O2a (M95) is a
human Y-chromosome DNA haplogroup. Haplogroup O2a is a descendent branch of
Haplogroup O2. Its closest extant phylogenetic relatives are the Haplogroup O2* Y-chromosomes found at a low frequency throughout most of East Eurasia and the
Haplogroup O2b Y-chromosomes found at low frequencies among the indigenous populations of
Inner Mongolia and
Manchuria and at much higher frequencies in
Korea and
Japan.
Haplogroup O2a is distributed widely in Asia, from southern
India to the
Altai Mountains and
Central Asia in the west, and from
Indonesia to northern
China and
Japan in the east. It is found only at marginally low frequencies of approximately 1% at the periphery of its distribution in southern India, Central Asia, northern China, and Japan, but many populations within the vast intervening territory in South Asia, Southeast Asia, and southern China display a greatly elevated frequency of Haplogroup O2a Y-chromosomes. Patrilines within Haplogroup O2a predominate among the
Austro-Asiatic populations of South and Southeast Asia, such as the
Khmer of Cambodia and the
Khasi of
Meghalaya in northeastern India. Some researchers have reported that slightly over half of all men in a composite sample of Austro-Asiatic speakers belonged to Haplogroup O2a.
Haplogroup O3 (M122), which attains its peak frequency among the
Sino-Tibetan and
Hmong-Mien peoples of
China and
Southeast Asia, and
Haplogroup O1a (M119), which predominates among
Taiwanese aborigines and many populations of the
Philippines, also generally occur among speakers of Austro-Asiatic languages in South China and the Indochinese Peninsula, but usually at much lower frequencies than Haplogroup O2a. The hypothesis that Haplogroup O2a was the major Y-chromosome haplogroup of the proto-Austro-Asiatic population is strengthened by the fact that Haplogroup O2a is the only haplogroup found among many Austro-Asiatic-speaking tribes, such as the
Juang of mainland India and the
Shompen of the
Nicobar Islands.
Haplogroup O2a has also been found to occur at a rather high frequency among the
Daic-speaking peoples of
Thailand and neighboring areas, which may reflect assimilation of the older Austro-Asiatic
Mon-Khmer populations that have left ample evidence of their presence in the region prior to the immigration of Daic speakers.
Outside of the region in which Austro-Asiatic languages are currently spoken or have a historically attested presence, Haplogroup O2a reaches its highest frequencies among the populations of the islands of
Sumatra,
Java,
Bali, and
Borneo in western and central
Indonesia. Haplogroup O2a has been found to be by far the most common Y-chromosome haplogroup among the
Balinese, occurring in approximately 58.6% (323/551) of a sample of Balinese men; Haplogroup O1a-M119 and Haplogroup O3-M122, which are typical of
Austronesian peoples outside of Malaysia and Indonesia, were observed in only 18.1% (100/551) and 6.9% (38/551) of Balinese men. Haplogroup O2a has also been found to be the most frequently occurring haplogroup among
Malay men in Singapore. The reason for its substantial presence in these populations, all of which are
Austronesian-speaking, is yet to be elucidated.
Subgroups
The
subclades of Haplogroup O2a with their defining mutation, according to the 2006 ISOGG tree:
- *O2a1 (M88, M111) Frequently found among Hani, She people, Tai peoples, Cambodians, and Vietnamese, with a moderate distribution among Qiang, Hlai, Miao, Yao, Taiwanese aborigines, populations of Borneo, and Han Chinese of Sichuan, Guangxi, and Guangdong
- **O2a1a (PK4) Found at low frequency among Pashtuns, Tharus,
[Simona Fornarino, Maria Pala, Vincenza Battaglia ]et al., "Mitochondrial and Y-chromosome diversity of the Tharus (Nepal): a reservoir of genetic variation," BMC Evolutionary Biology 2009, 9:154. and tribals of Andhra Pradesh
