Macro-haplogroup L (mtDNA)

In human mitochondrial genetics, L is the mitochondrial DNA macro-haplogroup that is at the root of the human mtDNA phylogenetic tree. As such, it represents the most ancestral mitochondrial lineage of all currently living modern humans.

Macro-haplogroup L's origin is connected with Mitochondrial Eve, and thus, is believed to suggest an ultimate African origin of modern humans. Its major sub-clades include L0, L1, L2, L3, L4, L5 and L6, with all non-Africans exclusively descended from just haplogroup L3.

Haplogroup L3 descendants notwithstanding, the designation "haplogroup L" is typically used to designate the family of mtDNA clades that are most frequently found in Sub-Saharan Africa. However, all non-African haplogroups coalesce onto either haplogroup M or haplogroup N, and both these macrohaplogroups are simply sub-branches of haplogroup L3. Consequently, L in its broadest definition is really a paragroup containing all of modern humanity, and all human mitochondrial DNA from around the world are subclades of haplogroup L. Haplogroups M and N are sometimes referred to as haplogroups L3M and L3N respectively. Mitochondrial Eve is defined as the female human ancestor who is the most recent common ancestor of the most deep-rooted lineages of humanity: haplogroups L, L0 and L1-6.

Origin

Studies of human mitochondrial (mt) DNA genomes demonstrate that the root of the human phylogenetic tree occurs in sub-Saharan Africa. The data suggest that Tanzanians have high genetic diversity and possess ancient mtDNA haplogroups, some of which are either rare or absent in other regions of Africa. A large and diverse human population has persisted in eastern Africa and that region may have been an ancient source of dispersion of modern humans both within and outside of Africa.^[2]

Mitochondrial Eve is the ancestor of this macro-haplogroup and she is estimated to have lived approximately 190,000 years ago.^[1]

Distribution

Putting aside its sub-branches, haplogroups M and N, L haplogroups are predominant all over sub-Saharan Africa; L is at 96-100%, apart from spreading areas of Afroasiatic languages, where it is lower. Low frequencies are in North Africa, Arabian Peninsula, Middle East and Europe.

Sub-Saharan Africa

With the exception of a number of lineages that returned to Africa from Eurasia after the out of Africa migration, all Sub-Saharan African lineages belong to haplogroup L. The "back-to-Africa" haplogroups including U6, X1 and possibly M1 have returned to Africa possibly as far back as 45,000 years ago.^[3] Haplogroup H, which is common among Berbers, is also believed to have entered Africa from Europe during the post post-glacial expansion.^[4]

The mutations that are used to identify the basal lineages of haplogroup L, are ancient and may be 150,000 years old. The deep time depth of these lineages entails that substructure of this haplogroup within Africa is complex and, at present, poorly understood.^[5] The first split within haplogroup L occurred 140-200kya, with the mutations that define macrohaplogroups L0 and L1-6. These two haplogroups are found throughout Africa at varying frequencies and thus exhibit an entangled pattern of mtDNA variation. However the distribution of some subclades of haplogroup L is structured around geographic or ethnic units. For example the deepest clades of haplogroup L0, L0d and L0k are almost exclusively restricted to the Khoisan of southern Africa. L0d has also been detected among the Sandawe of Tanzania, which suggests an ancient connection between the Khoisan and East African populations.^[6]

Macro-haplogroup L (mtDNA) composition within Africa. Approximate frequencies in: 1. North Africa.^[7][8] 2. Sudan.^[8] 3. Ethiopia.^[8][9] 4. West Africa.^[7] 5. East Africa (Kenya, Uganda, Tanzania).^[8][10][11] 6. Southeast Africa (Mozambique).^[12] 7. Native Southern Africans (!Xung, !Kung and Khwe khoisans).^[10][13] 8. Mbenga Pygmies (Baka, Bi-Aka and Ba-Kola).^[10][14] 9. Ba-Mbuti Pygmies.^[10] 10. Hadza/Sandawe.^[10]

North Africa

Haplogroup L is also found at moderate frequencies in North Africa. For example, the various Berber populations have frequencies of haplogroup L lineages that range from 3% to 45%.^[15][16] Haplogroup L has also been found at a small frequency of 2.2% in North African Jews from Morocco, Tunisia and Libya. Frequency was the highest in Libyan Jews 3.6%.^[17]

West Asia

Haplogroup L is also found in West Asia at low to moderate frequencies, most notably in Yemen where frequencies as high as 60% have been reported.^[18] It is also found at 15.50% in Bedouins from Israel, 13.68% in Palestinians, 12.55% in Jordania, 9.48% in Iraq, 9.15% in Syria, 6.66% in Saudi Arabia, 2.84% in Lebanon, 2.60% in Druzes from Israel, 2.44% in Kurds and 1.76% in Turks.^[17][19][20]

Europe

In Europe, haplogroup L is found at low frequencies, typically less than 1% with the exception of Iberia where frequencies as high as 18.2% have been reported and some regions of Italy where frequencies between 2 and 3% have been found.

Overall frequency in Iberia is higher in Portugal than in Spain where frequencies only high in the south and west of the country. Increasing frequencies are observed for Galicia (3.26%) and northern Portugal (3.21%), through the center (5.02%) and to the south of Portugal (11.38%).^[21] Relatively high frequencies of 7.40% and 8.30% was also reported respectively in South Iberia, in the present population of Huelva and Priego de Cordoba by Casas et al. 2006.^[22] Significant frequencies were also found in the Autonomous regions of Portugal, with L haplogroups constituting about 13% of the lineages in Madeira and 3.4 % in the Azores. In the spanish archipelago of Canary Islands, frequencies have been reported at 6.6%.^[23] According to some researchers L lineages in Iberia are associated to Islamic invasions, while for others it may be due to more ancient processes as well as more recent ones through the introduction of these lineages by means of the modern slave trade. The highest frequency (18.2%) of Sub-Saharan lineages found so far in Europe were observed by Alvarez et al. 2010 in the comarca of Sayago which is according to the authors "comparable to that described for the South of Portugal".^[24][25]

In Italy, Haplogroup L lineages are present in some regions at frequencies between 2 and 3% in Latium (2.90%), parts of Tuscany,^[19] Basilicata and Sicily.^[26]

The Americas

Haplogroup L lineages are found in the African diaspora of the Americas as well as indigenous Americans. Haplogroup L lineages are predominant among African Americans, Afro-Caribbeans and Afro-Latin-Americans. In Brazil, Pena et al. report that 85% of self-identified Afro-Brazilians have Haplogroup L mtDNA sequences.^[27] Haplogroup L lineages are also found at moderate frequencies in self-identified White Brazilians. Alves Silva reports that 28% of a sample of White Brazilians belong to haplogroup L.^[28] In Argentina, a minor contribution of African lineages was observed throughout the country.^[29] Haplogroup L lineages were also reported at 8% in Colombia,^[30] and at 4.50% in North-Central Mexico.^[31] In North America, haplogroup L lineages were reported at a frequency of 0.90% in White Americans of European ancestry.^[32]

Haplogroup L Frequencies (> 1%)

See also

• Recent African origin of modern humans

References

External links

• PhyloTree.org - mtDNA subtree L, Macro-haplogroup L by van Oven & Kayser M.
• Ian Logan's Mitochondrial DNA Site
• Cambridge DNA's An mtDNA view of the peopling of the world by Homo sapiens
• Behar DM, Villems R, Soodyall H, et al. (May 2008). "The dawn of human matrilineal diversity". American Journal of Human Genetics 82 (5): 1130–40. doi:10.1016/j.ajhg.2008.04.002. PMC 2427203. PMID 18439549. 
• Salas A, Richards M, De la Fe T, et al. (November 2002). "The making of the African mtDNA landscape". American Journal of Human Genetics 71 (5): 1082–111. doi:10.1086/344348. PMC 385086. PMID 12395296.