A 9-loci Y chromosome haplotype in three Italian populations.

Three geographic areas of Italy have been sampled and genotyped for 9 Y chromosome STRs: DYS19, DYS385, DYS388, DYS389 I and II, DYS390, DYS391, DYS392, DYS393. Sampling was focused on residents of small areas, well distant from major urban centres. Only individuals whose grandfather would live in the same area were included. A total of 210 unrelated individuals were collected. Distribution of genetic variation across the three samples and comparison with previously published Italian database indicated that so far Y chromosome diversity has been only partially explored in the Italian Peninsula.

Typing of 20 Y-chromosome STRs in the Italian population.

The aim of the present study is to appraise the increase of the discrimination power of the Y-specific haplotype allowed by 20 STR markers in a sample of the Italian population. The set of Y STR markers analyzed includes the European "extended haplotype" DYS19, DYS385, DYS389I/II, DYS390, DYS391, DYS392, DYS393 and YCAII a/b and in addition the DYS437, DYS438, DYS439, DYS447, DYS448, DYS388, DYS426, DYS460 (Y-GATA-A7.1) and Y-H4 loci.

Y chromosome genetic variation in the Italian peninsula is clinal and supports an admixture model for the Mesolithic-Neolithic encounter.

The Italian peninsula, given its geographical location in the middle of the Mediterranean basin, was involved in the process of the peopling of Europe since the very beginning, with first settlements dating to the Upper Paleolithic. Later on, the Neolithic revolution left clear evidence in the archeological record, with findings going back to 7000 B.C. We have investigated the demographic consequences of the agriculture revolution in this area by genotyping Y chromosome markers for almost 700 individuals from 12 different regions. Data analysis showed a non-random distribution of the observed genetic variation, with more than 70% of the Y chromosome diversity distributed along a North-South axis. While the Greek colonisation during classical time appears to have left no significant contribution, the results support a male demic diffusion model, even if population replacement was not complete and the degree of Neolithic admixture with Mesolithic inhabitants was different in different areas of Italy.

The analysis of variation of mtDNA hypervariable region 1 suggests that Eastern and Western Pygmies diverged before the Bantu expansion.

The Eastern Pygmies from Zaire and Western Pygmies from Cameroon, Congo, and the Central African Republic represent the two principal groups of African Pygmies. In the "recent divergence" hypothesis in which Western Pygmies are thought to be the result of hybridization between the ancestors of Eastern Pygmies and Bantu farmers who penetrated the equatorial belt and came into contact with Pygmies around 2-3 kiloyears ago. On the basis of recent archaeological research in the tropical rain forest, we propose a "pre-Bantu divergence" hypothesis, which posits the separation between the ancestors of Eastern and Western Pygmies earlier than 18 kiloyears ago. In order to test the two hypotheses, we analyzed the variation of the hypervariable region 1 of the mitochondrial DNA in the Mbenzele, Western Pygmies of the Central African Republic, and compared our results with those of previous mtDNA and Y chromosome studies. Distribution, sequence variation, and age of haplogroups along with genetic distances among populations, estimates of divergence times, and simulations based on the coalescent approach were found to be congruent with the pre-Bantu divergence but failed to support the recent divergence hypothesis.

A study of Y-chromosome microsatellite variation in sub-Saharan Africa: a comparison between F(ST) and R(ST) genetic distances.

Seven Y-chromosome microsatellite loci (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, and DYS393) were analyzed in three populations from sub-Saharan Africa: the Bamileke and Ewondo populations from Cameroon and the Hutu from Rwanda. Complete typing was obtained for 112 individuals, and a total of 53 different haplotypes was observed. The single-locus gene diversity, averaged across populations, ranges from 0.100 for the DYS392 locus to 0.610 for the DYS389I locus. The haplotype diversity ranges from 0.832 (Ewondo) to 0.965 (Hutu), with an intermediate value of 0.918 in the Bamileke. The diversity among Bamileke, Ewondo, Hutu, and other sub-Saharan populations selected from the literature was analyzed using both a classical (F(ST)) and a stepwise-based (R(ST)) genetic distance method. The pattern of interpopulational diversity based on F(ST) was congruent with anthropological knowledge, while that based on R(ST) revealed unexpected and unconvincing population affinities. From a practical point of view, our study indicates that Y-chromosome microsatellite data may provide useful information for analyses of interpopulational diversity among sub-Saharan populations if an adequate number of loci and individuals along with an appropriate genetic distance method are used. On a theoretical ground, we propose that the lesser performance of R(ST) compared to F(ST) could be explained by the important role played by genetic drift in shaping the relationships among examined populations.

Variation of female and male lineages in sub-Saharan populations: the importance of sociocultural factors.

In this paper, we present a study of genetic variation in sub-Saharan Africa, which is based on published and unpublished data on fast-evolving (hypervariable region 1 of mitochondrial DNA and six microsatellites of Y chromosome) and slow-evolving (haplogroup frequencies) polymorphisms of mtDNA and Y chromosome. Our study reveals a striking difference in the genetic structure of food-producer (Bantu and Sudanic speakers) and hunter-gatherer populations (Pygmies, Kung, and Hadza). In fact, the ratio of mtDNA to Y-chromosome Nupsilon is substantially higher in food producers than in hunter-gatherers as determined by fast-evolving polymorphisms (1.76 versus 0.11). This finding indicates that the two population groups differ substantially in female and male migration rate and/or effective size. The difference also persists when linguistically homogeneous populations are used and outlier populations are eliminated (1.78 vs 0.19) or when the jacknife procedure is applied to a paired population data set (1.32 to 7.84 versus 0.14 to 0.66). The higher ratio of mtDNA to Y-chromosome Nnu in food producers than in hunter-gatherers is further confirmed by the use of slow-evolving polymorphisms (1.59 to 7.91 versus 0.12 to 0.35). To explain these results, we propose a model that integrates demographic and genetic aspects and incorporates ethnographic knowledge. In such a model, the asymmetric gene flow, polyginy, and patrilocality play an important role in differentiating the genetic structure of sub-Saharan populations. The existence of an asymmetric gene flow is supported by the phylogeographic features of mtDNA and Y-chromosome haplogroups found in the two population groups. The role of polyginy and patrilocality is sustained by the evidence of a differential pressure of genetic drift and gene flow on maternal and paternal lineages of food producers and hunter-gatherers that is revealed through the analysis of mitochondrial and Y-chromosomal intrapopulational variation.

Binary and microsatellite polymorphisms of the Y-chromosome in the Mbenzele pygmies from the Central African Republic.

This study analyzes the variation of six binary polymorphisms and six microsatellites in the Mbenzele Pygmies from the Central African Republic. Five different haplogroups (B2b, E(xE3a), E3a, P and BR(xB2b,DE,P)) were observed, with frequencies ranging from 0.022 (haplogroup P) to 0.609 (haplogroup E3a). A comparison of haplogroup frequencies indicates a close genetic affinity between the Mbenzele and the Biaka Pygmies, a finding consistent with the common origin and the geographical proximity of the two populations. The haplogroups P, BR(xB2b,DE,P) and E(xE3a), which are rare in sub-Saharan Africa but common in western Eurasia, were observed with frequencies ranging from 0.022 (haplogroup P) to 0.087 (haplogroup E(xE3a)). Thirty different microsatellite haplotypes were detected, with frequencies ranging from 0.022 to 0.152. The Mbenzele share the highest percent of microsatellite haplotypes with the Biaka Pygmies. Five out seven haplotypes which are shared by the Mbenzele and Biaka Pygmies belong to haplogroup E3a, which suggests that they are of Bantu origin. The plot based on F(st) genetic distances calculated using microsatellite data provides a picture of population relationships which is in part congruent and in part complementary to that obtained using haplogroup frequencies. Finally, the Mbenzele and Biaka Pygmies were found to be markedly more genetically similar using Y-chromosomal than autosomal microsatellites. We suggest that this could be due to the higher phylogenetic stability of Y-chromosome and to the effect of the male-biased gene flow during the Bantu expansion.