Abstract An analysis of 11 Alu insertion polymorphisms (ACE, TPA25, PV92, APO, FXIIIB, D1, A25, B65, HS2.43, HS3.23, and HS4.65) has been performed in several NW African (Northern, Western, and Southeastern Moroccans; Saharawi; Algerians; Tunisians) and Iberian (Basques, Catalans, and Andalusians) populations. Genetic distances and principal component analyses show a clear differentiation of NW African and Iberian groups of samples, suggesting a strong genetic barrier matching the geographical Mediterranean Sea barrier. The restriction to gene flow may be attributed to the navigational hazards across the Straits, but cultural factors must also have played a role. Some degree of gene flow from sub-Saharan Africa can be detected in the southern part of North Africa and in Saharawi and Southeastern Moroccans, as a result of a continuous gene flow across the Sahara desert that has created a south-north cline of sub-Saharan Africa influence in North Africa. Iberian samples show a substantial degree of homogeneity and fall within the cluster of European-based genetic diversity.
The population history of North Africa is particularly interesting because, although the region belongs to continental Africa, its history has been completely different from the sub-Saharan part. The peopling of the region has been influenced by two strong geographical barriers: the Sahara Desert to the south, which splits the African continent into two differentiated regions, and the Mediterranean Sea to the north, which separates the European and African continents. These geographical barriers may have constrained human movements in North Africa into an east-west gradient, although they were not impermeable to human movements. During the first half of the Holocene, the humid climate that prevailed in the Sahara produced a receding of the desert allowing human settlements, but over the past 5000 years, the Sahara Desert has suffered a gradual aridification and has become as dry as it is nowadays (Said and Faure 1990). Historical records document extensive trade routes that were established across the desert between sub-Saharan Africa and the north coast. In contrast, since the time of the Phoenicians, the city-based settlement pattern of the NW African coast integrated the area into the Mediterranean world. The seaward orientation of populations persisted and, similar to the desert, separated the Maghreb (NW Africa) from the rest of Africa to the south (Newman 1995). Moreover, during the 8th century AD, Berbers from North Morocco and Algeria under Arab leadership crossed the Mediterranean Sea and occupied the Iberian Peninsula for almost eight centuries, although the demographic impact of the conquest is thought to be limited (Hitti 1990).
Until recently, few genetic studies have been performed in NW Africa. In the latest compilation of classical genetic markers in North Africa (Bosch et al. 1997), the first principal component (PC) of gene frequencies showed an east-west pattern of genetic differentiation, in agreement with the geographical barrier imposed by the Sahara and the Mediterranean. Recent work with autosomal short tandem repeats (STRs; Bosch et al. 2000), mitochondrial DNA (mtDNA) sequences (Rando et al. 1998), and Y-chromosome haplotypes (Bosch et al. 1999) has suggested that the gene flow between NW Africa and Iberia and that between sub-Saharan Africa and NW Africa has been small. MtDNA variation in NW Africa (Rando et al. 1998) has shown a high frequency (up to 25%) of geographically specific sequences (named haplogroup U6) that is essentially absent in the Iberian Peninsula (from 0% in Andalusians to 5% in Portuguese). The mtDNA analysis has shown a limited gene flow from Europe to NW Africa that could be attributed to recent human movements.The study of Y-chromosome haplotypes (Bosch et al. 1999) shows little admixture between NW Africa and the Iberian Peninsula. The study of 21 autosomal STR loci in NW Africa has also shown a clear genetic difference between NW African populations and Iberians, although some degree of gene flow into Southern Iberia (Andalusians) can be detected (Bosch et al. 2000).
There are a large number of Alu insertion polymorphisms throughout the human genome; these are rapid and easy to type, apparently selectively neutral, and have known ancestral states. The insertion of an Alu element into the human genome is almost certainly a unique event, making any pair of Alu insertion alleles identical by descent and free of homoplasy (Batzer and Deininger 1991; Batzer et al. 1994; Stoneking et al. 1997). The use of these polymorphisms in a world-wide survey of human populations has confirmed the African origin of modern humans (Batzer et al. 1994, 1996; Stoneking et al. 1997). However, the use of Alu insertion polymorphisms in human evolution has been focused world-wide, and except for some population studies (Novick et al. 1998), relatively little research has been devoted to specific population questions. We have analyzed several NW African and Iberian populations for 11 Alu insertion polymorphisms, three of which have not been analyzed in previous worldwide population studies, in order: (1) to determine the genetic differentiation of the Alu insertion polymorphisms in NW African populations; (2) to compare the genetic composition of NW African and Iberian populations, establishing the possible amount of gene flow between them; and (3) to detect possible admixture from sub-Saharan African populations into NW Africa. The use of polymerase chain reaction (PCR)-based neutral autosomal DNA polymorphisms whose frequencies are only dependent on drift and migration (and not mutation) and whose ancestral state is known is a novel and powerful tool for the study of human populations.
Another ‘Berbers are essentially Eurasian, but not closely related to Europeans’ DNA study. I shall have to stick this one on my ‘Eurasian origin of the Berbers’ DNA page. In essence, Berbers are essentially Caucasian, not closely related to Europeans, and have been in North Africa for about 30,000 years with a refresher wave of near eastern colonists arriving in Morocco about 10,000 years ago and a few later.
There’s an interesting display on this link that deals with Mt DNA with attention paid to North Africa in particular.