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Haplogroup U6 (mtDNA)


Geographic distribution

Haplogroup U6 has a very wide geographic distribution across the northern half of Africa, the Middle East and most of western and southern Europe. It has been found at low frequencies as far north as the Baltic and as far east as Central Asia and Iran. It is most common in North-West Africa, especially among the Mozabites (28%) and Kabyles (18%) of Algeria, as well as Mauritanians (14%) and Canary Islanders (13.5%). Other regions with frequencies of U6 exceeding 1% include 6-8% in Morocco and coastal Algeria, 5% in Tunisia, 4% in Libya, 2.5% in Lebanon, Portugal, Egypt and Oman, 2% in Cyprus, Sudan, Ethiopia and Guinea-Bissau, 1.5% in Saudi Arabia, and 1% in Syria, Jordan and in Spain.

Isolated pockets of high U6 frequencies have been reported in Iberia, notably 8.5% in Huelva (western Andalusia) by Hernández et al. 2014, 7% in northern Portugal by Pereira et al. 2000, 4.3% in northern Portugal, 4% in central Spain and 2.5% in central Portugal by Ottoni et al. 2011, and 2.6% in Catalonia by by Garcia et al. 2011.

U6 is only found at trace frequencies among Ashkenazi Jews and in most of Europe. The highest frequencies observed in Europe outside Iberia are in south-west France (1.4%), Brittany (0.7%), in Tuscany (0.6%), Sicily (0.5%) and southern Italy (0.5%).

Distribution of mtDNA haplogroup U6 in Europe, North Africa and the Middle East

Distribution of mtDNA haplogroup U6 in Europe, North Africa and the Middle East

Origins & History

Although now found primarily in western, northern and north-eastern Africa, haplogroup U6 descends from the western Eurasian haplogroup U, and therefore represents a back migration to Africa. Secher et al. (2014) estimated that U6 arose very approximately 35,000 years ago (±11 ky), during the Early Upper Paleolithic, and prior to the Last Glacial Maximum (LGM).

The oldest and largest subclade, U6a, would have appeared around the LGM. U6a lineages are thought to have spread in several waves across North Africa, probably starting around 20,000 years ago, following the northern coastline of Africa. Several U6a branches (U6a1, U6a3, U6a6, U6a6b, U6a7, and U6a7b) appear to have expanded within the Maghreb from 20,000 years ago, with some spreading to the Iberian Peninsula (U6a1, U6a1b).

U6b, U6c and U6d emerged later, some time between 13,000 and 10,000 years ago, from the end of the Last Glacial period.

Neolithic expansion

U6a and U6b lineages underwent the most spectacular expansion since the Neolithic period, spreading from the Maghreb to West Africa (U6a3c, U6a3f, U6a5, U6b) and the Canary Islands (U6b1a), and crossing the Sahara all the way to the Sudan to Arabia (U6a3d). This expansion might have been carried by the arrival of domesticated cattle from the Middle East by men belonging to Y-haplogroup R1b-V88 as U6b is typically found in herding populations in which both R1b-V88 and U6b are present, including the Berbers of the Maghreb, the Fulani people of the Sahel and the Hausa people of Sudan. R1b-V88 cattle herders are believed to have started advancing into northern Africa during the Neolithic Subpluvial (c. 7250 BCE to 3250 BCE), when the Sahara was considerably wetter and greener than today, and would have reached the Maghreb by 4,500 BCE. Consequently, the expansion of R1b-V88 with the assimilated Maghreban lineages of that period (mostly H1, H3, U6 and HV0/V) would have taken place from c. 6,000 years ago, and may have continued until fairly recently in some regions.

Canary Islands

Ancient mitochondrial DNA analysis of the Guanches, the aboriginal population of the Canary Islands, conducted by Maca-Meyer et al. (2003) and Fregel et al. (2009) confirmed the presence of mtDNA U6b1a and U6c1 in the archipelago prior to the European colonisation (alongside haplogroups HV0, H, J, K, L, N1b, T2c, W and X). Acheological evidence indicates that the Canary Islands were first settled c. 2,500 years ago.

Subclades

  • U6
    • U6a'b'd
      • U6a: found in western and northern Africa, western Europe, the Middle East and the Horn of Africa
        • U6a1:
          • U6a1a: found in the Maghreb, Iberia and southern Italy
          • U6a1b: found in the Maghreb, Iberia, Italy, France, Belgium and Scandinavia
        • U6a2
          • U6a2a: found in Ethiopia
          • U6a2b: found in Ethiopia and the Arabian peninsula
          • U6a2c: found in Armenia, Egypt and Portugal
        • U6a3
          • U6a3a: found in the Maghreb and Iberia
            • U6a3a1: found in the Maghreb, Iberia and Finland
            • U6a3a2: found in the Maghreb, Iberia and Germany
          • U6a3c: found in Ghana
          • U6a3d: found in Egypt and Palestine
          • U6a3e: found in the Maghreb and Iberia
          • U6a3f: found in Guinea-Bissau, Burkina Faso and Nigeria
        • U6a4: found in Iraq and Italy
        • U6a5: found in the Maghreb, Iberia, Italy, Hungary, Chad, Cameroon and Nigeria
          • U6a5a
          • U6a5b
        • U6a6
          • U6a6a: found in Morocco
          • U6a6b: found in Morocco and Tunisia
        • U6a7
          • U6a7a
            • U6a7a1: found in France, Italy and Mauritania
              • U6a7a1a: found among the Acadians
              • U6a7a1b: found among Sephardic Jews
            • U6a7a2: found in Britain
          • U6a7b: found in Algeria, Tunisia, France and Britain
          • U6a7c: found in Tunisia
        • U6a8: found in the Maghreb
          • U6a8a: found in the Maghreb
          • U6a8b: found in the Maghreb and Spain
        • U6b'd
        • U6b: found mostly in southwest Asia, West Africa and Iberia
          • U6b1: found in northern Spain and the Canaries
          • U6b2: found in Morocco and Spain
          • U6b3: found in Morocco, Portugal and Spain
        • U6d: found mostly in the Maghreb and Iberia
          • U6d1: found mostly in the Maghreb
            • U6d1a: found in Britain
            • U6d1b: found in the Maghreb and southern Italy
          • U6d2: found in Algeria and Ethiopia
          • U6d3: found in Morocco, Portugal and Spain
    • U6c : found mostly in the northern Maghreb and southwest Europe
      • U6c1: found in Italy and the Canaries
      • U6c2: found in Morocco and France


Associated medical conditions

Rollins et al. (2009) examined the association between brain pH and mtDNA alleles. The highest brain pH was found in members of haplogroups U and K. Higher pH confers protection against Parkinson's disease and psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder. Another study by the University of Manchester suggests that a lower brain acidity (i.e. higher pH) has a protective effect against strokes. Research on intelligence point that people with higher IQ tend to have more alkaline brains. Higher pH is associated with better conductivity-transmission between neurons (source).

Hendrickson et al. (2008) studied the role played by mitochondrial function in AIDS progression in HIV-1 infected persons. They found that AIDS progression was slower for members of haplogroups U and K, except for U6a which had a faster progression.

The T16189C polymorphism, defining haplogroups U6a1a, U6a2, U6a3, U6a6a, U6a7c, U6a8, U6b1b and U6c lowers the rate of mtDNA replication and consequently the number of mtDNA copies, reducing metabolic efficiency. It has been linked to maternally inherited thinness (Parker 2005), thinness at birth (Soini 2012) and increased body mass index (Liou 2007), and increased frequency of type 2 diabetes in the UK (Poulton 2002) and in Asia (Weng 2005 and Park 2008).

The common C150T mutation has been found at strikingly higher frequency among Chinese and Italian centenarians and may be advantageous for longevity and resistance to stress according to Chen et al. (2012). C150T defines haplogroups U6a3f, U6a4, U6a7a1b and U6c.

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