Alu insertion polymorphisms in NW Africa and the Iberian Peninsula: evidence for a strong genetic boundary through the Gibraltar Straits

An analysis of II Alu insertion polymorphisms (ACE, TPA25, PV92, APO, FXIII B, D1, A25, B65, HS2.43, HS3.23. and HS4.65) has been pet-formed in several NW African (Northern,Western, and Southeastern Moroccans; Saharawi; Algeri ans; Tunisians) and Iberian (Basques, Catalans, and Andalusians) population s. Genetic distances and principal component analyses show a clear differen tiation of NW African and Iberian groups of samples, suggesting a strong ge netic barrier matching the geographical Mediterranean Sea barrier. The rest riction to gene flow may be attributed to the navigational hazards across t he Straits, but cultural factors must also have played a role. Some degree of gene flow from sub-Saharan Africa tan be detected in the southern part o f North Africa and in Saharawi and South-eastern Moroccans, as a result of a continuous gene flow across the Sahara desert that has coated a south-nor th dine of sub-Saharan Africa influence in North Africa. Iberian samples sh ow a substantial degree of homogeneity and fall within the cluster of Europ ean-based genetic diversity.