North African genes in Iberia studied by Y-chromosome DNA haplotype 5

Human Biology, Oct 2001 by Lucotte, Gerard, Gerard, Nathalie, Mercier, Geraldine

In our own present data concerning southwest European frequencies, haplotype 15 frequencies are heterogeneous among the five populations studied (X^sup 2^ = 97.15; degrees of freedom [df] = 4), a statistically significant value (> 9.49) with p

The study of variations in the frequency of haplotype 5, the second most frequent (31.6%) haplotype (Table 1), is the main purpose of the present study. The most elevated value obtained for haplotype 5 in our series was for Berbers (68.9%), and percentages of haplotype distributions show a gradient of decreasing frequency north from Morocco: 40.8% in Andalusia, 36.2% in Portugal, 12.1% in Catalonia, and 11.3% in the Basque region. Haplotype 5 frequencies are heterogeneous among the five populations tested (X^sup 2^ = 88.97); there is a significant (p

Haplotype 5, the "Berber haplotype" (Lucotte et al. 2000), therefore allows assessment of the patrilineal North African gene flow into Iberia. For the corresponding matrilineal gene flow, mitochondrial DNA (mtDNA) analyses have already shown that the Iberian Peninsula is differentiated in terms of levels of genetic diversity and presence of unique lineage groups (forte-Real et al. 1996). In this last study it might be considered that the North African Berber branch had some input into Iberia (quantified as approximately 10% in Spanish mtDNA lineages, 7% in Portuguese, and none in Basque).

Initial studies on genetic markers corresponding to nuclear gene frequencies in human populations in the Iberian Peninsula (Bertranpetit and CavalliSforza 1991; Calafell and Bertranpetit 1993) have shown that the first principal component (PC) of gene frequencies (the percentage of variation explained by this factor being 27.1%) is that between people originally of Basque and nonBasque descent. The second PC (14.5% of variation explained, and 41.6% cumulated) points to the genetic divergence between Catalonia and the central and south central parts of Iberia. The third PC (12.3%, and 53.9% cumulated) concerns the Mediterranean as opposed to the Atlantic regions. The fourth and fifth factors cover a reasonable portion of variance (9.6% and 9.0%, respectively), but they were more difficult to interpret. No factor examined in these studies seems to involve the southern Iberian Peninsula, and the authors concluded that it was unlikely that the North African genetic contribution would be easily detectable by these methods of analysis.

In fact, a more recently published synthesis (Arnaiz-Villena et al. 1999), based on genetic markers in Basques, Portuguese, Spaniards, and North Africans, supports substantial gene flow from paleo-North African populations to Iberia. Some genetic studies, in particular on the HLA system (Amaiz-Villena et al. 1995; Martinez-Laso et al. 1995; Amaiz-Villena et al. 1997), have shown Iberian populations to be more closely related to North African populations than to the rest of Europe. In a recent study (G6mez-Casado et al. 2000), Moroccan Algerians show the closest genetic distance-based on HLA class I (A and B) and class II (DRB 1) markers-followed by Berbers, Spaniards, and Basques. North African input into Iberia may be close to 20%, as shown by nuclear CD4/Alu markers (Flores et al. 2000b). It seems that the significance of the genetic links detected between North Africa and Iberia reflect both an ancient common substratum (Arnaiz-Villena et al. 1999) and, to a lesser degree, possible contacts between Christians and North African Muslims (A.D. 710-1492) in Iberia (Kandil et al. 1999), who had a Berber genetic substratum.