Origin and Diffusion of mtDNA Haplogroup X

Origin and Diffusion of mtDNA Haplogroup X

AbstractA 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.
Further northeast of the Altai area, haplogroup X sequences were detected in the Tungusic-speaking Evenks, of the Podkamennaya Tunguska basin (Central Siberia). In contrast to the Altaians, the Evenks did not harbor any West Eurasian mtDNA haplogroups other than X. However, neither of the two Evenk X haplotypes showed mutations characteristic of the Native American clade X2a. Instead, one sequence was a member of X2b and the other of X2* (fig. 2). Thus, one possible scenario is that several X haplotypes arrived in Siberia from western Asia during the Palaeolithic, but only X2a crossed Beringia and survived in modern Native Americans. Alternatively, the presence of two phylogenetically different haplogroup X mtDNA sequences in this particular subpopulation of Evenks might be due to recent gene flow

Part of my attempt to get to grips with the phantom ancestor of X2a. I have to say, that I find accepting an East Asian source for the X2 hard, and it’s largely to do with the dates that X2 as a hg has. If the coalescence of the entire X2 Hg is somewhere between 20 to 30k, and seems to be focused in West Asia, then how it managed to move itself so fast over all of Asia to colonise America via Siberia is a bit of a mystery, particularly since it seemed to do so without leaving a trace there. It seems the possibility it came across the Atlantic ocean is very unpopular.

7 responses to “Origin and Diffusion of mtDNA Haplogroup X

  1. It has been proposed by the Smithsonian institute that ancient Solutreans from Southern France and Spain , may have crossed the Atlantic some 17000 years ago, taking with them the mtDNA haplogroup X.
    At that time the North Atlantic was frozen due to the ice age permitting these ancient peoples to cross over contributing to the first inhabitants of ancient North America.
    There has also been a documentary on the television about it, which goes into more depth on the study.

  2. Further northeast of the Altai area, haplogroup X sequences were detected in the Tungusic-speaking Evenks, of the Podkamennaya Tunguska basin (Central Siberia). In contrast to the Altaians, the Evenks did not harbor any West Eurasian mtDNA haplogroups other than X. However, neither of the two Evenk X haplotypes showed mutations characteristic of the Native American clade X2a. Instead, one sequence was a member of X2b and the other of X2* (fig. 2). Thus, one possible scenario is that several X haplotypes arrived in Siberia from western Asia during the Palaeolithic, but only X2a crossed Beringia and survived in modern Native Americans.

    Totally agree. Seems the most likely scenario and we should consider oruselves fortunate that some Evenks have carried these clades into the modern era.

    If the coalescence of the entire X2 Hg is somewhere between 20 to 30k, and seems to be focused in West Asia, then how it managed to move itself so fast over all of Asia to colonise America via Siberia is a bit of a mystery…

    This coalescence age would seem a little bit young to me (I tend to be sceptic of TRMC age estimates, as you know). We must remember that X is a direct descendant of N, one of the two oldest Eurasian haplogroups, from which it’s separated by 6 or 7 SNPs (one varies, ref) and that it coalesced in West Eurasia probably c. 50,000 years ago, if not before (N might be West Eurasian after all if we follow the diversity clue, and there were AMHs in West Eurasia since more than 100,000 years ago). X1 and X2 are separated by a much smaller ammount of SNPs, suggesting a rather rapid split after the coalescence of X as such.

    I certainly find no real problem for X2 being present in Siberia (and hence in Beringia) before the Clovis expansion some 11,000 years ago (expansion that was surely the one behind the arrival of mtDNA X2 to America). The relative lack of traces is only puzzling up to a point, considering that North Asia always had an extremely low population density (causing extreme drift) and that recent demic migrations (Turks, Russians) have radically reduced the native diversity as well.

  3. PS- Also notice that while the TRMCA estimate for X is of c. 20,000 years, the date considered for X1 is of 42,000 years. This [age(X1)>age(X)] is such an obvious imposibility that all the equation should be considered invalid (and the overall premises for TRMCA estimation too).

  4. What do you think of this?

    “Using comparisons of thousands of ancient and modern skulls, collected over a period of 20 years and containing new data from Mongolia that became accessible just last summer, Prof Loring Brace showed how the native inhabitants of the Western Hemisphere fit into several different groups based on craniofacial patterns. Their studies show that descendants of the first humans to enter the New World, including natives of Mexico, Peru, and the southern United States, have no obvious ties to any Asian groups. He said: “This could be because they have been separated from their Asian sources for the longest period of time.”

    A second group – including the Blackfoot, Iroquois, and other tribes from Minnesota, Michigan, Ontario, and Massachusetts – was descended from the Jomon, the prehistoric people of Japan. The Inuit appear to be a later branch from that same Jomon trunk. Tribal groups who lived down the eastern seaboard into Florida share this origin, according to prof Brace. Another group, originating in China and including the Athabascan-speaking people of the Yukon drainage of Alaska and north-west Canada, spread as far south as Arizona and northern Mexico.”

  5. If I may, I am a lay person interested in this Haplogroup X anomalous ‘puzzle’ of its geographic distribution (That is just something I do for fun – find intriguing puzzles in science and read up on them and follow developments. This one I’ve been trying to follow for close on a decade now.)

    For a small beginning, I note this:

    Further northeast of the Altai area, haplogroup X sequences were detected in the Tungusic-speaking Evenks, of the Podkamennaya Tunguska basin (Central Siberia).

    Reference to Tunguska raised an eyebrow. That is, of course, the site of the 1908 blast that also has been a puzzle for a century now. One observation I recall reading (sorry I cannot point to a source) long ago was of Soviet scientists noting botanical DNA disturbances that they associated with the blast.

    This immediately brought the question to mind if there would be any possibility that the blast had been considered as affecting the Haplogroup X findings with the Evenk people? Is it something that has been ruled out by the data?

    A second question: Luis, you state

    This [age(X1)>age(X)] is such an obvious imposibility [sic] that all the equation [sic?] should be considered invalid (and the overall premises for TRMCA estimation too).

    Your point is clear, that a child cannot be older than its parent. I only know the datings from my occasional reading, but is there any chance at all that the assignment of X as the root of the X tree might be wrong, and that the mutation was in the other direction, making X1 the real root of the X tree? Might it be too early to tell? I bring it up because I am slightly familiar with some problems in paleontology with determining which human ancestors came in what order. Is the genetic data base large enough to determine without question that X preceded X1?

    Thanks for whatever answers come.

    (I am glad to find new web pages on this topic. I’d had to leave it for quite some time, and it is enjoyable to catch up.)

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