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In human mitochondrial genetics, Haplogroup X is a human mitochondrial DNA (mtDNA) haplogroup which can be used to define genetic populations. The genetic sequences of haplogroup X diverged originally from haplogroup N, and subsequently further diverged about 20,000 to 30,000 years ago to give two sub-groups, X1 and X2. Overall haplogroup X accounts for about 2% of the population of Europe, the Near East and North Africa. Sub-group X1 is much less numerous, and restricted to North and East Africa, and also the Near East. Sub-group X2 appears to have undergone extensive population expansion and dispersal around or soon after the last glacial maximum, about 21,000 years ago. It is more strongly present in the Near East, the Caucasus, and Mediterranean Europe; and somewhat less strongly present in the rest of Europe. Particular concentrations appear in Georgia (8%), the Orkney Islands (in Scotland) (7%) and amongst the Israeli Druze (26%); the latter are presumably due to a founder effect.

North and South America

Haplogroup X is also one of the five haplogroups found in the indigenous peoples of the Americas.^[1] Although it occurs only at a frequency of about 3% for the total current indigenous population of the Americas, it is a major haplogroup in northern North America, where among the Algonquian peoples it comprises up to 25% of mtDNA types. It is also present in lesser percentages to the west and south of this area -- in North America among the Sioux (15%), the Nuu-Chah-Nulth (11%?13%), the Navajo (7%), and the Yakima (5%), and in South America among the Yanomami people (12%) in eight villages in Roraima in northwestern Brazil.

Unlike the four main Native American haplogroups (A, B, C, and D), X is not at all strongly associated with East Asia. The sole occurrence of X in Asia discovered so far is in Altaia in South Siberia (Derenko et al, 2001), and detailed examination (Reidla et al, 2003) has shown that the Altaian sequences are all almost identical, suggesting that they arrived in the area probably from the South Caucasus more recently than 5000 BP.

This absence of haplogroup X2 in Asia is one of the major factors causing the current rethinking of the peopling of the Americas. However, the New World haplogroup X2a is as different from any of the Old World X2b-f lineages as they are from each other, indicating an early origin "likely at the very beginning of their expansion and spread from the Near East".^[2]

The Solutrean Hypothesis posits that haplogroup X reached North America with a wave of European migration about 20,000 BP by the Solutreans, a stone-age culture in south-western France and in Spain, by boat around the southern edge of the Arctic ice pack.

Another possible way to explain existence of haplogroup X in mtDNA of indigenous peoples of the Americas is that it was brought to North America with the people of Caucasian origin through the Bering land bridge. ^[3]

References

• Andrea K. C. Ribeiro-Dos Santos; S. E. B. Santos; A. L. Machado; V. Guapindaia; and M. A. Zago 1996. Heterogeneity of Mitochondrial DNA haplotypes in pre-Columbian Natives of the Amazon Region. American Journal of Physical Anthropology 101:29-37 (1996).
• Peter N. Jones 2004. American Indian mtDNA, Y Chromosome Genetic Data, and the Peopling of North America. Boulder: Bauu Press.
• RD Easton, DA Merriwether et al, mtDNA variation in the Yanomami: evidence for additional New World founding lineages. American Journal of Human Genetics, 59(1):213-225 (1996)
• Michael D. Brown et al, mtDNA Haplogroup X: An Ancient Link between Europe/Western Asia and North America?, American Journal of Human Genetics, 63:1852-1861 (1998)
• David Glenn Smith et al, Distribution of mtDNA Haplogroup X among Native North Americans, American Journal of Physical Anthropology 110:271-284 (1999)
• Miroslava V. Derenko et al, The Presence of Mitochondrial Haplogroup X in Altaians from South Siberia American Journal of Human Genetics, 69(1):237?241 (2001)
• Maere Reidla et al, Origin and Diffusion of mtDNA Haplogroup X, American Journal of Human Genetics, 73:1178?1190 (2003)
• Ilia A. Zaharov et al, Mitochondrial DNA Variation in the Aboriginal Populations of the Altai-Baikal Region: Implications for the Genetic History of North Asia and America Annals of the New York Academy of Sciences 1011: 21 (2004)

See also

• Human mitochondrial DNA haplogroups
• Human mitochondrial genetics
• Models of migration to the New World
• In his popular book The Seven Daughters of Eve, Bryan Sykes named the originator of this mtDNA haplogroup "Xenia".

External links

• X mt-Haplogroup project at FTDNA
• Spread of Haplogroup X, from National Geographic
• Coming into America: Tracing the Genes, PBS, popular presentation of the Solutrean hypothesis

cs:Haploskupina X (mtDNA)