Mitochondrial DNA variation of southern Tunisian populations

Due to its complex history of migrations and colonization of African, European and Asian people, the Tunisian territory is an ideal area to study the effects of cultural change on the genetic structure of human populations. We investigated the mtDNA genetic variation of Tunisian populations in order to detect the possible impact of recent historical events on their gene pool. Two Arab and three Berber communities were analysed using a comparison dataset of 45 other populations including African, Arabian, Asian, European and Near Eastern groups. The results obtained were compared with those produced using a large panel of autosomal SNPs. We observed a slight but important difference between the populations that inhabit the southern and central-northern areas of the country. Furthermore, robust signatures of genetic isolation were detected in two Berber populations (Nouvelle Zraoua and Tamezret) and in the seminomadic Arab group of the R’Baya. Our investigation suggests that the genetic structure of investigated southern Tunisian populations retains signatures of historical events which occurred between 7th-17th century, particularly the trans-Saharan slave trade and the emigration of Berbers in remote areas of the south during the Arab conquest

Berbers and Arabs. Tracing the genetic diversity and history of Southern Tunisia through genome wide analysis

Objectives: Tunisia has been a crossroads for people from Africa, Europe, and the Middle East since prehistoric times. At present, it is inhabited by two main ethnic groups, Arabs and Berbers, and several minorities. This study aims to advance knowledge regarding their genetic structure using new population samplings and a genome-wide approach. Materials and Methods: We investigated genomic variation, estimated ancestry components and dated admixture events in three Berber and two Arab populations from Southern Tunisia, mining a dataset including Middle Eastern, sub-Saharan, and European populations. Results: Differences in the proportion of North African, Arabian, and European ancestries and the varying impact of admixture and isolation determined significant heterogeneity in the genetic structure of Southern Tunisian populations. Admixture time estimates show a multilayer pattern of admixture events, involving both ethnolinguistic groups, which started around the mid XI century and lasted for nearly five centuries. Discussion: Our study provides evidence that the relationships between genetic and cultural diversity of old and new inhabitants of North Africa in southern Tunisia follow different patterns. The Berbers seem to have preserved a significant part of their common genomic heritage despite Islamization, Arab cultural influence, and linguistic diversity. Compared to Morocco and Algeria, southern Tunisian Arabs have retained a higher level of Arabian ancestry. This is more evident in the semi-nomad R'Baya, who have kept their original Bedouin lifestyle, than in the population from Douz, who have undergone multiple events of stratification and admixture

Overcoming the dichotomy between open and isolated populations using genomic data from a large European dataset

Human populations are often dichotomized into "isolated" and "open" categories using cultural and/or geographical barriers to gene flow as differential criteria. Although widespread, the use of these alternative categories could obscure further heterogeneity due to inter-population differences in effective size, growth rate, and timing or amount of gene flow. We compared intra and inter-population variation measures combining novel and literature data relative to 87,818 autosomal SNPs in 14 open populations and 10 geographic and/or linguistic European isolates. Patterns of intra-population diversity were found to vary considerably more among isolates, probably due to differential levels of drift and inbreeding. The relatively large effective size estimated for some population isolates challenges the generalized view that they originate from small founding groups. Principal component scores based on measures of intra-population variation of isolated and open populations were found to be distributed along a continuum, with an area of intersection between the two groups. Patterns of inter-population diversity were even closer, as we were able to detect some differences between population groups only for a few multidimensional scaling dimensions. Therefore, different lines of evidence suggest that dichotomizing human populations into open and isolated groups fails to capture the actual relations among their genomic features

A report of four different unusual 6-PGD electrotypes in Caucasian and Negro populations

Four different unusual 6-phosphogluconate dehydrogenase (6-PGD) electrophoretic patterns found among the Italian (Rome), Bamileke (Cameroon), and North Bateke and Babenga Pygmy (Congo) populations are described

Testing a Biochemical Model of Human Genetic Resistance to falciparum Malaria by the Analysis of Variation at Protein and Microsatellite Loci

We recently proposed a biochemical model of genetic resistance to falciparum malaria based on the role of oxidant stress (of parasitic origin) in inducing the irreversible oxidation of hemoglobin and its binding to the erythrocyte membrane (Destro-Bisol et al. 1996). To test the model, we analyzed the relationships between the polymorphisms at the hemoglobin beta chain (.HBB) and red cell glutathione peroxidase (GPX1) loci in 18 populations that had been subjected to endemic malaria (Cameroon and Central African Republic). The erythrocytes of GPX1*2 heterozygotes should be more efficient in sheltering the cell membrane from irreversible oxidation and binding of hemoglobin caused by the oxidant stress exerted by Plasmodium falciparum. According to our model, the GPX1*2 allele has an epistatic effect on the HBB*A/*S genotype by lowering its protection againstfalciparum malaria. In turn, this should decrease the fitness of the HBB*A/*S-GPX1 *2/*l genotype. Our predictions were confirmed. In fact, we observed a clear trend toward a dissociation between the HBB*A/*S and GPX1 *2/*l genotypes in the overall data. To test alternative hypotheses, we also analyzed the genetic variation at 9 protein and 10 autosomal microsatellite loci at both the single- and the 2-locus level. We also discuss the possible relevance of an alternative biochemical pathway. The results further support the conclusions of our study because the dissociation between the GPX1 *2/*l and HBB *A/*S genotypes does not appear to be related either to a general decrease in heterozygosity or to an increased risk of sudden death in HBB*A/*S individuals

Testing a biochemical model of human genetic resistance to falciparum malaria by the analysis of variation at protein and microsatellite loci

We recently proposed a biochemical model of genetic resistance to falciparum malaria based on the role of oxidant stress (of parasitic origin) in inducing the irreversible oxidation of hemoglobin and its binding to the erythrocyte membrane (Destro-Bisol et al. 1996). To test the model, we analyzed the relationships between the polymorphisms at the hemoglobin beta chain (HBB) and red cell glutathione peroxidase (GPX1) loci in 18 populations that had been subjected to endemic malaria (Cameroon and Central African Republic). The erythrocytes of GPX1*2 heterozygotes should be more efficient in sheltering the cell membrane from irreversible oxidation and binding of hemoglobin caused by the oxidant stress exerted by Plasmodium falciparum. According to our model, the GPX1*2 allele has an epistatic effect on the HBB*A/*S genotype by lowering its protection against falciparum malaria, In turn, this should decrease the fitness of the HBB*A/*S-GPX1*2/*1 genotype. Our predictions were confirmed, in fact, we observed a clear trend toward a dissociation between the HBB*A/*S and GPX1*2/*1 genotypes in the overall data. To test alternative hypotheses, we also analyzed the genetic variation at 9 protein and 10 autosomal microsatellite loci at both the single- and the 2-locus level, We also discuss the possible relevance of an alternative biochemical pathway, The results further support the conclusions of our study because the dissociation between the GPX1*2/*1 and HBB*A/*S genotypes does not appear to be related either to a general decrease in heterozygosity or to an increased risk of sudden death in HBB*A/*S individuals

Frequencies at CD4, FES, and F13A1 microsatellite loci in central-southern Sardinia (Italy)

We have analyzed the distribution of allele frequencies at three microsatellite loci (CD4, FES, and F13A1) among individuals living and born in central-southern Sardinia (Italy), in a zone called "Trexenta" within the province of Cagliari (n = 50). This area has been already studied from the linguistic and genetic point of view (1) using classical polymorphism at protein level. Informed consent was obtained from all donors