Haplogroup X (mtDNA)

In human mitochondrial genetics, Haplogroup X is a human mitochondrial DNA (mtDNA) haplogroup found in Native Americans, Europeans, and Western Asians.

Origin

mtDNA-based chart of possible large human migrations.

The genetic sequences of haplogroup X diverged originally from haplogroup N, and subsequently further diverged about 30,000 years ago^[2] to give two sub-groups, X1 and X2.

Distribution

Haplogroup X is found in approximately 7% of native Europeans,^[3] and 3% of all Native Americans from North America.^[4]

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 is largely 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 community (27%). Subclades X2a and X2g are found in North America, but are not present in native South Americans.^[5]

Druze

The greatest frequency of haplogroup X is observed in the Druze, a minority population in Israel, Jordan, Lebanon, and Syria, as much in X1 (16%) as in X2 (11%).^[6] The Druze also have much diversity of X lineages. This pattern of heterogeneous parental origins is consistent with Druze oral tradition. The Galilee Druze represent a population isolate, so their combination of a high frequency and diversity of X signifies a phylogenetic refugium, providing a sample snapshot of the genetic landscape of the Near East prior to the modern age.^[7]

North America

Haplogroup X is also one of the five haplogroups found in the indigenous peoples of the Americas.^[8] Although it occurs only at a frequency of about 3% for the total current indigenous population of the Americas, it is a bigger haplogroup in northern North America, where among the Algonquian peoples it comprises up to 25% of mtDNA types.^[9][10] It is also present in lesser percentages to the west and south of this area—among the Sioux (15%), the Nuu-Chah-Nulth (11%–13%), the Navajo (7%), and the Yakama (5%).^[11]

Unlike the four main Native American mtDNA haplogroups (A, B, C, D), and the Y-chromosome sub-haplogroup Q1a3a, X is not at all strongly associated with East Asia. The main occurrence of X in Asia discovered so far is in the Altay people in Southwestern Siberia,^[12] and detailed examination^[6] has shown that the Altaian sequences are all almost identical (haplogroup X2e), suggesting that they arrived in the area probably from the South Caucasus more recently than 5,000 BP.

Earlier (2001) research indicated that Altaians have maintained their native identity and only begun, very recently, to mix with groups (mostly Russians and Kazakhs) who do not show mtDNA haplogroup X. Genetic studies and researchers show, "the analysis of the tribal structure of Southern Altaians has shown that the present-day Altaians have retained their native language and ethnic identity. They have begun to mix with other ethnic groups (mostly Russians and Kazakhs) only recently, so the interethnic admixture is estimated to be <5% (Luzina 1987; Osipova et al. 1997). The haplogroup X mtDNAs have not been found in populations of central Asia, including Kazakhs, Uighurs, and Kirghizs (Comas et al. 1998). Since the frequency of haplogroup X in Russians is extremely low (3 of 336; Orekhov et al. 1999; Malyarchuk and Derenko 2000; authors’ unpublished data), the recent European admixture cannot explain the presence of haplogroup X in the Altaians. Hence, the results of the present study allow us to suggest that haplogroup X was the part of the ancestral gene pool for Altaian populations, being found both in northern and southern Altaians."^[12]

In addition, these same (2001) researchers indicated that the mtDNA haplogroup X haplotype present in the Altaians of Siberia is intermediate between Native Americans clades and that of Europeans. As a Russian research group observed, "American Indian and European haplogroup X mtDNAs ... are distantly related to each other". They propose however not an early European colonization of America, but that Altaians contributed to migrants bound for Europe and America; "The network further suggests that the Altaian X haplotypes occupy the intermediate position between European and American Indian haplogroup X mtDNA lineages"^[12] However, further research in 2003 indicated that the haplotype present in the Altaians is not intermediate between Native American clades and that of Europeans, and that the Native Americans probably split early from the others, with the split occurring "likely at the very beginning of their expansion and spread from the Near East, ... around, or after, the Last Glacial Maximum when the climate ameliorated".^[6]

One theory of how the X Haplogroup ended up in North America is it migrated from central Asia along with the A, B, C, and D Haplogroups, from an ancestor from the Altai Region of Central Asia.^[13] Two sequences of haplogroup X2 were sampled further east of Altai among the Evenks of Central Siberia.^[6] These two sequences belong to X2* and X2b. It is uncertain if they represent a remnant of the migration of X2 through Siberia or a more recent input.^[13]

This relative 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, X2c, X2d, X2e, and X2f 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".^[13]

The Solutrean Hypothesis postulates that haplogroup X reached North America with a wave of European migration about 20,000 BP by the Solutreans,^[14][15] a stone-age culture in south-western France and in Spain, by boat around the southern edge of the Arctic ice pack.

In a 2008 article in the American Journal of Human Genetics, a group of researchers in Brazil (except for David Glenn Smith, of U.C. Davis) argue against the Solutrean hypothesis, stating: "Our results strongly support the hypothesis that haplogroup X, together with the other four main mtDNA haplogroups, was part of the gene pool of a single Native American founding population; therefore they do not support models that propose haplogroup-independent migrations, such as the migration from Europe posed by the Solutrean hypothesis ... Here we show, by using 86 complete mitochondrial genomes, that all Native American haplogroups, including haplogroup X, were part of a single founding population, thereby refuting multiple-migration models." ^[11]

Subclades

Tree

This phylogenetic tree of haplogroup X subclades is based on the paper by Mannis van Oven and Manfred Kayser Updated comprehensive phylogenetic tree of global human mitochondrial DNA variation^[1] and subsequent published research.

• X
  • X1
    • X1a
      • X1a1
    • X1b
  • X2
    • X2a
      • X2a1
        • X2a1a
        • X2a1b
      • X2a2
    • X2b
      • X2b1
      • X2b2
      • X2b3
      • X2b4
    • X2c
      • X2c1
      • X2d
    • X2e
      • X2e1
        • X2e1a
          • X2e1a1
            • X2e1a1a
      • X2e2
        • X2e2a
    • X2f
    • X2g
    • X2h

Popular culture

In his popular book The Seven Daughters of Eve, Bryan Sykes named the originator of the European-American subset of this mtDNA haplogroup - corresponding to X2 - "Xenia".

See also

• Genealogical DNA test
• Genetic Genealogy
• Human mitochondrial genetics
• Population Genetics
• Human mitochondrial DNA haplogroups
• Indigenous American genetic studies

External links

• General
  • Mannis van Oven's – mtDNA subtree N
• Haplogroup X
  • The Presence of Mitochondrial Haplogroup X in Altaians from South Siberia Miroslava V. Derenko, Tomasz Grzybowski, and others ^[12]
  • Ian Logan's DNA Site
  • Carolyn Benson's X mtDNA Project at Family Tree DNA
  • Spread of Haplogroup X, from National Geographic

References