October 21, 2003

Origin and Diffusion of mtDNA Haplogroup X

Am. J. Hum. Genet., 73:000, 2003

Maere Reidla et al.

A maximum parsimony tree of 21 complete mitochondrial DNA (mtDNA) sequences belonging to haplogroup X and the survey of the haplogroup-associated polymorphisms in 13,589 mtDNAs from Eurasia and Africa revealed that haplogroup X is subdivided into two major branches, here defined as "X1" and "X2." The first is restricted to the populations of North and East Africa and the Near East, whereas X2 encompasses all X mtDNAs from Europe, western and Central Asia, Siberia, and the great majority of the Near East, as well as some North African samples. Subhaplogroup X1 diversity indicates an early coalescence time, whereas X2 has apparently undergone a more recent population expansion in Eurasia, most likely around or after the last glacial maximum. It is notable that X2 includes the two complete Native American X sequences that constitute the distinctive X2a clade, a clade that lacks close relatives in the entire Old World, including Siberia. The position of X2a in the phylogenetic tree suggests an early split from the other X2 clades, likely at the very beginning of their expansion and spread from the Near East.


Virtually all (97.2%) haplogroup X mtDNAs from the Near East, the South Caucasus, and Europe were found to belong to subhaplogroup X2, as did all (100%) of those from Siberia and Central Asia and some (36.8%) of those from North Africa (table 2). Thus, subhaplogroup X2 is characterized by a very wide geographic range but also by an infrequent occurrence. Indeed, it generally comprises <5% of the mtDNAs in West Eurasian and North African populations (table 1). Three exceptions include the Druze, the Georgians, and the Orkney Islanders, among whom the frequency of X2 reaches 11%, 8%, and 7%, respectively. The high frequencies of X2 in the Druze and the Orkney Islanders are combined with a low haplotype diversity (0.400 and 0.473, respectively), and the relatively high frequency in these populations is most likely due to genetic drift and founder events. Overall, it appears that the populations of the Near East, the Caucasus, and Mediterranean Europe harbor subhaplogroup X2 at higher frequencies than those of northern and northeastern Europe (P < .05) and that X2 is rare in Eastern European as well as Central Asian, Siberian, and Indian populations and is virtually absent in the Finno-Ugric and Turkic-speaking people of the Volga-Ural region.


The results of this study point to the following conclusions. First, haplogroup X variation is completely captured by two ancient clades that display distinctive phylogeographic patternsX1 is largely restricted to North and East Africa, whereas X2 is spread widely throughout West Eurasia. Second, it is apparent that the Native American haplogroup X mtDNAs derive from X2 by a unique combination of five mutations. Third, the few Altaian (Derenko et al. 2001) and Siberian haplogroup X lineages are not related to the Native American cluster, and they are more likely explained by recent gene flow from Europe or from West Asia. Fourth, the split between "African" X1 and "Eurasian" X2 subhaplogroups of X is phylogenetically as deep as that within the branches of haplogroup U that also differ profoundly in their phylogeography. Thus, subhaplogroup U6 is largely restricted to North Africa (as X1), whereas subhaplogroup U5 is widespread in West Eurasia (as X2). The phylogeographic patterns and the coalescence times that we obtained here suggest that the basic phylogenetic structures of the mtDNA haplogroups in West Eurasia and North Africa are as ancient as the beginning of the spread of anatomically modern humans in this region. Finally, phylogeography of the subclades of haplogroup X suggests that the Near East is the likely geographical source for the spread of subhaplogroup X2, and the associated population dispersal occurred around, or after, the LGM when the climate ameliorated. The presence of a daughter clade in northern Native Americans testifies to the range of this population expansion.


Posted by Dienekes at October 21, 2003 04:46 PM | PermaLink

Could you help me determine what clade I might belong to? My MtDNA results are as follows;

Haplogroup X





Any thoughts or references would be greatly appreciated.

An X without roots...

Sean Davis

Posted by: Sean Davis at January 29, 2004 07:14 AM

Hi! I read your site, and I was wondering: are you implying that Native Aericans could be descended from the Near East more than Siberia?

Posted by: bernard viniot at May 4, 2004 02:00 AM

Native Americans are descended from prehistoric Siberians, but they also have a particular haplogroup that is not found in Siberians, but is found in the Near East, establishing a very old link between the two regions.

Posted by: Dienekes at May 4, 2004 12:45 PM

The "particular haplogroup" you are speaking of is Haplogroup X, which *HAS* been found in certain Siberian populations (primarily in the Altai peoples, at a level comparable to that in Europe & the Americas) back in 2001, and more recently at a lower level in several neighboring tribal groups.

Posted by: Kenuchelover at May 10, 2004 02:38 PM

Haplogroup X did not originate in Siberia. It is lacking in most Siberians. It was brought to Siberia and from there to the New World from the Near East.

Posted by: Dienekes at May 12, 2004 12:39 AM

Haplogroup X belongs to both Europe and the First Nations because a part of those people were some of the first to cross the bridge. Their migration took them as far as the "Eastern Sea" and there, they settled. Those of the same group left behind, also embarked upon another migration, this time to the west and so X is found - just as rarely - in some European populations.
In the Americas, X is found in about 1 - 3% of mostly Anishnaabeg or Ojibwe with some testing finding it also in other Eastern Nations. If your mother's, mother's, mother knew this land, you belong. One drop of blood in a river is still a drop of blood.

Posted by: Dawn at July 12, 2004 06:37 PM
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