February 21, 2013

Algerian Y chromosomes and mtDNA

From the paper:
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
It would be interesting to estimate the depth of common ancestry of the North African "European" Y chromosomes to determine the epoch during which they arrived there, i.e., whether the common ancestry stems from recent historical contacts (Roman Empire, Vandals, etc.) or from the early settlement of both Mediterranean coasts during the arrival of R-M269 into Europe.


A few observations on Y-haplogroup frequencies:

  • The ubuquity of haplogroup Q at trace frequencies in most regions except North Africa (only a little in ALG) is interesting and it's high time that someone looked at the relationship between West Eurasian Q-bearers and their much more numerous East Eurasian cousins.
  • I find the paucity of Y-haplogroup I in North Africa noteworthy; given its high levels in most of Western Europe, its relative absence might indicate that the people who brought "European" R-M269 into N Africa were not occasional recent migrants, but rather earlier settlers. 
  • The relative absence of J2 is expected, given that neither of the two main strata of population ("Berber" and "Arab") may have possessed it initially; it has also not been found in a historical sample from the Canary Islands, whereas its J1 counterpart has.
  • The paucity of haplogroup G, which is the European Neolithic lineage par excellence probably argues against the involvement of the people who colonized Europe during the Early Neolithic in similar events on the south shore of the Mediterranean.
  • The further study of F chromosomes could also be further attempted, given their possible involvement in the Upper Paleolithic of Eurasia

The authors highlight that 80% of mtDNA is Eurasian vs. 90% of Y chromosomes. This might point to asymmetric gene flow from Sub-Saharan Africa. Alternatively, it might point to some mtDNA that is characterized as non-Eurasian (because it does not belong to the M, N macro-haplogroups) being in fact so. It is a persistent question whether lineages that have a wide frequency differential in two regions do so because of gene flow (from the high- to low-frequency area), or because of other processes.

PLoS ONE 8(2): e56775. doi:10.1371/journal.pone.0056775

Introducing the Algerian Mitochondrial DNA and Y-Chromosome Profiles into the North African Landscape

Asmahan Bekada et al.

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. The presence of East-West and North-South haplogroup frequency gradients strongly reinforces the genetic complexity of this region. However, this genetic scenario is beset with a notable gap, which is the lack of consistent information for Algeria, the largest country in the Maghreb. 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%). In spite of these sexual asymmetries, the Algerian uniparental profiles faithfully correlate between each other and with the geography.

Link

5 comments:

Daniel Kalina said...

The y-dna sample from Libya is mostly Tuarag not representative of libya.Libya is only 5% Tuareg. THe most interesting thing is the possible presence of R-V88 IN Mauritania they clustereded Mauritania with West Sahara the studies showed no R-V88 in west Sahara . Does this mean more than 10% of those in Mauritania have R-V88Z?.

eurologist said...

The paucity of haplogroup G, which is the European Neolithic lineage par excellence probably argues against the involvement of the people who colonized Europe during the Early Neolithic in similar events on the south shore of the Mediterranean.

I believe there is archaeological evidence that some of the Early Neolithic, European Mediterranean settlers where also present in North Africa, but then left for Europe due to climatic reasons. Thus, it could be that there are simply not many traces left.

kalupitero said...

I don't understand something, the small chart shows E-M78 and R1b-M343, with they retested for new SNPs. You can see that MOR has 75 samples and TUN 120. But then the big graph shows 760 samples for MOR and 601 for TUN. So I presume most of the samples in the big graph didn't test for the new SNPs, and yet these untested SNPs are still shown in the chart. This should show up as a biased result, for example, M78* being too common and E-V22 or E-V65 too few, but that doesn't seem to be the case. Can someone explain what's going on? And yes, I did read the study, and I'm still not clear.

kalupitero said...

Here's a better example to explain my misunderstanding. The small graph says MOR has 75 samples and 3 are R1b-U152. The big graph says MOR has 760 samples and 2.63%, exactly 20 of them, are U152.

So did they test all the R1b from all the MOR samples for U152? But if they did, why didn't they include them all in the small graph? Furthermore, I don't recall any previous study testing for the new R1b SNPs in any country in North Africa (MOR = Morocco). This study is a first. So I'm completely confused.

mregdna said...

There was a lot of jews in the Oran/Tlemcen Area and also
Koulougis (descendants of Janissaries
and north-African women).
Maybe some of the J2, R1b, Q etc are related with them.