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Introducing the Algerian Mitochondrial DNA and Y-Chromosome Profiles into the North African Landscap
Published: February 19, 2013
North Africa is considered a distinct geographic and ethnic entity within Africa. Although modern humans originated in this Continent, studies of mitochondrial DNA (mtDNA) and Y-chromosome genealogical markers provide evidence that the North African gene pool has been shaped by the back-migration of several Eurasian lineages in Paleolithic and Neolithic times. More recent influences from sub-Saharan Africa and Mediterranean Europe are also evident.
To fill this gap, we analyzed a sample of 240 unrelated subjects from a northwest Algeria cosmopolitan population using mtDNA sequences and Y-chromosome biallelic polymorphisms, focusing on the fine dissection of haplogroups E and R, which are the most prevalent in North Africa and Europe respectively. The Eurasian component in Algeria reached 80% for mtDNA and 90% for Y-chromosome. However, within them, the North African genetic component for mtDNA (U6 and M1; 20%) is significantly smaller than the paternal (E-M81 and E-V65; 70%). The unexpected presence of the European-derived Y-chromosome lineages R-M412, R-S116, R-U152 and R-M529 in Algeria and the rest of the Maghreb could be the counterparts of the mtDNA H1, H3 and V subgroups, pointing to direct maritime contacts between the European and North African sides of the western Mediterranean. Female influx of sub-Saharan Africans into Algeria (20%) is also significantly greater than the male (10%).
Comparisons between North African and Mediterranean Europe maternal and paternal gene pools reveal sharp discontinuities and limited gene flow between both areas. Furthermore, Berbers constitute a very heterogeneous group showing significant differences even between geographically close communities. However, an unexpected lack of differentiation between Berber and Arab speaking communities was found.
Samples
Blood samples were anonymously obtained from a total of 240 unrelated healthy adult residents in northwest Algeria (Oran area) after informed written consent. This study was approved by the research ethics committee of the University of La Laguna. DNA was extracted using the standard salting-out method. For Y-Chromosome analysis, DNA from previous surveys were used for fine resolution analyses of haplogroups E1b (M78): 26 samples from Iberians and Moroccans [46], 6 from Algerians, and 4 from Tunisians, and for R1b (M343): 361 samples from Iberians and Moroccans, 13 from Saharawi and Mauritanians, 12 from Algerians, and 2 from Tunisians.
Results
Algerian mtDNA Profile
Mozabites are the most differentiated with a p<0.001 value in both comparisons, whereas the Oran-miscellaneous Algerian pair is only significantly different at p<0.05 level. A detailed inspection of their haplogroup profiles compared to those of surrounding populations (Supplementary Table S2) shows that Mozabites present a high excess of U3 and U6a1′2′3 haplotypes whereas the miscellaneous sample lacks HV0 representatives and has an outstanding excess of J/J1c/J2, L3e5 and L2a1 lineages.
However, in spite of their apparent differences, the three Algerian samples are joined as a tight cluster in a PCA analysis based on haplogroup frequencies (data not shown), and for this reason they have been pooled together for large-area comparisons. In addition, Andalusians from Tunisia show closer affinities with Moroccans and Algerians than with Tunisians (Figure 2A). In comparison with other Mediterranean and west Asian samples, the H haplogroup subdivision in the Algerian sample shows a typical Maghreb population structure (Supplementary Table S4). Congruently, the most common western subgroups, H1 (47.8%) and H3 (10.1%), represent 60% of H lineages. Furthermore, the H1 frequency in Algeria is intermediate between that found in Morocco (51.6%) and Tunisia (29.4%), fitting the eastward-decreasing gradient previously observed for this subgroup
Of all North African populations, Eurasian lineages are the most frequent in Algeria (80%) while sub-Saharan Africa origin accounts for the remaining 20%. At least two Eurasian lineages, M1 and U6, had Paleolithic implantation and subsequent expansions in North Africa, reaching the Sahel and Sudan belts.
Regarding the sub-Saharan African component, Algeria (20%) is at the same level as Morocco (20.4%) and Egypt (22.9%) but significantly lower (p = 0.003) than Tunisia (30.1%) and marginally lower (p = 0.059) than Libya (27.1%). Aside from the widespread haplogroup L2a, the majority (14%) of Algerian L lineages (L1b, L2a1, L2b, L2c, L3b, L3d) are of West Africa origin. Those from Central Africa (L1c, L3e, L3f) account for an additional 5%, leaving around 1% for those of East African ancestry (L0, L3*, L4). It has been suggested that these lineages reached North Africa since Holocene times, when climatic amelioration permeated the Saharan desert. However the historical trans-Saharan slave trade promoted by the Arabs may have been mainly responsible for their present day incidence.
Within North Africa, the Algerian lowest genetic distance is observed for Tunisia (FST = 0.016) and the greatest for Egypt (0.026). Italy (FST = 0.032) and the Balkans (FST = 0.032) are the closest areas within the European peninsulas while France is the most distant European region (FST = 0.042). Finally, for the Middle East, the Levant (FST = 0.014) seems to be the most similar and the Arabian Peninsula (FST = 0.033) the most different. In fact, removing the pairwise comparison between Algeria and Arabia, the mean FST value for the Middle East drops considerably (FST = 0.018+0.001) rising the mean distance of Algeria from Europe significantly compared to that from the Middle East (p<0.01).
Algerian Y-chromosome profile
Results for the sub-typing of haplogroups E-M78 and R-M343 in the Iberian Peninsula and Northwest African countries including Algeria are presented in Figure 1. In general, data for E-M78 agree with the previous analysis [41]. Therefore, the Eurasian E-V13 is the most common sub-group in Iberia, although one North African E-V65 type has also been detected. On the African side, the lack of E-M78 representatives in a total sample of 189 males from the W. Saharan-Mauritanian area is notable. For the Maghreb countries, the fact that the number of males belonging to para-group E-M78* is the same as those included in the autochthonous E-V65 group also stands out.
For the R-M343 subdivision, the Iberian Peninsula reflects a genuine European profile [45] except for the presence of one Sahel R-V88 type. In contrast, all R-M343 detected in W. Saharan-Mauritanian belong to sub-group R-V88, reaching a frequency of 7%, similar to those observed in other Sahel samples [40]. In the Maghreb countries, the frequency of R-V88 drops to around 1%. On the other hand, the presence in this area of representatives of the European sub-groups R-M412, R-S116, R-U152 and R-M529 points to North-South maritime contacts across the Mediterranean.
(Table S6) --> http://journals.plos.org/plosone/art...e.0056775.s006
Supplementary Table S6 presents frequencies of Y-chromosome haplogroups, as spread out as possible, for the same countries-areas as performed for the mtDNA analysis. Clearly, markers E-V65, E-M81 and J1-M267 confirm the geographic and ethnic identity of Algeria but, while E-M81 represents an autochthonous group that sharply decreases in Egypt, J1-M267 points to a Levantine influence. Haplogroups G-M201, L-M20, R2-M124, T-M70, J2-M172 and the majority of derived J2 sub-groups all reflect West Asian influences on Europe with only weak inputs on North Africa.
On their part, several European I sub-groups also extend to West Asia with minor gene flow to the African countries. Exceptions to this general pattern are the subgroups J2-M67 and R-M412 that have similar frequencies in Algeria as in Europe, and R2-M124 whose frequency in Egypt is not significantly different from the mean value of European and West Asian areas.
Within North Africa, the Maghreb region appears well differentiated from Egypt, which, reflecting its geographical position, is near to the Levant and the Arabian Peninsula. The most influential haplogroups in the first component separation are: E-M81, E-V65 and R-V88 that pull the North African countries together, and J-M172, R-M173, R-M17, R-M124 and R-L23 that pull West Asian countries in the opposite direction. In the second component, haplogroups R-L11, R-M529, R-U198, I-M223 and I-M26 are responsible for the spread of the European Mediterranean countries away from Egypt and Arabia, which in turn are pulled by J-M267, B-M60, E-V22 and E-M123.
(Table S8) --> http://journals.plos.org/plosone/art...e.0056775.s008
Pairwise based FST distances between populations were calculated (Supplementary Table S8). The mean FST values comparing the Algerians with the other North African samples (0.061+0.015), with Europeans (0.197+0.019) and with West Asians (0.159+0.011) also reflects its geographic position. Within North Africa, its lowest distance is to W. Sahara-Mauritania (FST = 0.023) and the greatest to Libya (FST = 0.108). Italy (FST = 0.155) is the closest of the European peninsulas and Iberia the most distant (FST = 0.247), while for West Asia, the Levant (FST = 0.128) is the most similar area to Algeria and the Caucasus the most different (FST = 0.194).
More --> http://journals.plos.org/plosone/art...l.pone.0056775
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Originally Posted by Gilgamesh900
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