Whole-genome sequence analysis of a Pan African set of samples reveals archaic gene flow from an extinct basal population of modern humans into sub-Saharan populations

BackgroundPopulation demography and gene flow among African groups, as well as the putative archaic introgression of ancient hominins, have been poorly explored at the genome level.ResultsHere, we examine 15 African populations covering all major continental linguistic groups, ecosystems, and lifestyles within Africa through analysis of whole-genome sequence data of 21 individuals sequenced at deep coverage. We observe a remarkable correlation among genetic diversity and geographic distance, with the hunter-gatherer groups being more genetically differentiated and having larger effective population sizes throughout most modern-human history. Admixture signals are found between neighbor populations from both hunter-gatherer and agriculturalists groups, whereas North African individuals are closely related to Eurasian populations. Regarding archaic gene flow, we test six complex demographic models that consider recent admixture as well as archaic introgression. We identify the fingerprint of an archaic introgression event in the sub-Saharan populations included in the models (similar to 4.0% in Khoisan, similar to 4.3% in Mbuti Pygmies, and similar to 5.8% in Mandenka) from an early divergent and currently extinct ghost modern human lineage.ConclusionThe present study represents an in-depth genomic analysis of a Pan African set of individuals, which emphasizes their complex relationships and demographic history at population level.Peer reviewe

Genetic heterogeneity in Algerian human populations

The demographic history of human populations in North Africa has been characterized by complex processes of admixture and isolation that have modeled its current gene pool. Diverse genetic ancestral components with different origins (autochthonous, European, Middle Eastern, and sub-Saharan) and genetic heterogeneity in the region have been described. In this complex genetic landscape, Algeria, the largest country in Africa, has been poorly covered, with most of the studies using a single Algerian sample. In order to evaluate the genetic heterogeneity of Algeria, Y-chromosome, mtDNA and autosomal genome-wide makers have been analyzed in several Berber- and Arab-speaking groups. Our results show that the genetic heterogeneity found in Algeria is not correlated with geography or linguistics, challenging the idea of Berber groups being genetically isolated and Arab groups open to gene flow. In addition, we have found that external sources of gene flow into North Africa have been carried more often by females than males, while the North African autochthonous component is more frequent in paternally transmitted genome regions. Our results highlight the different demographic history revealed by different markers and urge to be cautious when deriving general conclusions from partial genomic information or from single samples as representatives of the total population of a region.This study was supported by the Ministerio de Economía y Competitividad grant CGL2013-44351-P and by Direcció General de Recerca, Generalitat de Catalunya grant 2014SGR866

Y chromosome Analyses of Molecular Variance (AMOVA) in the Algerian samples.

<p>*** P<0.0001</p><p>* P<0.05; ns: not significant</p><p>North = Algiers, Oran, Tizi Ouzou</p><p>South = Mozabite, Reguibate, Zenata</p><p>Arabs = Reguibate, Algiers, Oran</p><p>Berbers = Zenata, Mozabite, Tizi Ouzou</p><p>^# Arabs without the Reguibate</p><p>Y chromosome Analyses of Molecular Variance (AMOVA) in the Algerian samples.</p

Correlation plots of the ancestry proportions at k = 4 in the ADMIXTURE analysis comparing autosomes and X-chromosome SNPs.

<p>North African, sub-Saharan, Middle Eastern, and European ancestry proportions are shown in different plots. Solid black lines represent linear correlations between autosomal and X-chromosome components.</p

mtDNA Analyses of Molecular Variance (AMOVA) in the Algerian samples.

<p>*** P<0.0001; ns: not significant</p><p>North = Algiers, Oran (both)</p><p>South = Mozabite, Reguibate, Zenata</p><p>Arabs = Reguibate, Algiers, Oran1, Oran2</p><p>Berbers = Zenata, Mozabite</p><p>^# Arabs without the Reguibate</p><p>mtDNA Analyses of Molecular Variance (AMOVA) in the Algerian samples.</p

Geographic location of the Algerian samples genotyped in the present study (in red) and the samples obtained from the literature (in yellow).

<p>Geographic location of the Algerian samples genotyped in the present study (in red) and the samples obtained from the literature (in yellow).</p

Plots for the analysis of genome-wide SNPs.

<p>PC analysis (upper figures) based on autosomal data, and X-chromosome SNPs. ADMIXTURE proportions (bottom figures) at k = 2,3, and 4 based on autosomal data and X-chromosome SNPs. Algeria, stands for general Algerian sample [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138453#pone.0138453.ref003" target="_blank">3</a>]; Mozabite, stands for the Algerian Berber Mozabites [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138453#pone.0138453.ref032" target="_blank">32</a>]; and Zenata, stands for Algerian Berber Zenata (present study).</p

Bidimensional plots based on uniparental genomes.

<p>PC analyses based on haplogroup data for Y-chromosome and mtDNA; and MDS analyses based on Y-STR haplotype data and on mtDNA sequence data. Abbreviations: ALG/ALG1: Algiers (this study), ALG2: Algiers (Y-chromosome; [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138453#pone.0138453.ref010" target="_blank">10</a>]), ORN1: Oran (present study), ORN2: Oran (Y-chromosome, [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138453#pone.0138453.ref021" target="_blank">21</a>]; mtDNA, [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138453#pone.0138453.ref017" target="_blank">17</a>]), RGB: Reguibate, ZNT: Zenata, MZB: Mozabite, TZO: Tizi Ouzou</p

European Roma groups show complex West Eurasian admixture footprints and a common South Asian genetic origin

The Roma population is the largest transnational ethnic minority in Europe, characterized by a linguistic, cultural and historical heterogeneity. Comparative linguistics and genetic studies have placed the origin of European Roma in the Northwest of India. After their migration across Persia, they entered into the Balkan Peninsula, from where they spread into Europe, arriving in the Iberian Peninsula in the 15th century. Their particular demographic history has genetic implications linked to rare and common diseases. However, the South Asian source of the proto-Roma remains still untargeted and the West Eurasian Roma component has not been yet deeply characterized. Here, in order to describe both the South Asian and West Eurasian ancestries, we analyze previously published genome-wide data of 152 European Roma and 34 new Iberian Roma samples at a fine-scale and haplotype-based level, with special focus on the Iberian Roma genetic substructure. Our results suggest that the putative origin of the proto-Roma involves a Punjabi group with low levels of West Eurasian ancestry. In addition, we have identified a complex West Eurasian component (around 65%) in the Roma, as a result of the admixture events occurred with non-proto-Roma populations between 1270-1580. Particularly, we have detected the Balkan genetic footprint in all European Roma, and the Baltic and Iberian components in the Northern and Western Roma groups, respectively. Finally, our results show genetic substructure within the Iberian Roma, with different levels of West Eurasian admixture, as a result of the complex historical events occurred in the Peninsula

Recent historical migrations have shaped the gene pool of arabs and berbers in North Africa

North Africa is characterized by its diverse cultural and linguistic groups and its genetic heterogeneity. Genomic data has shown an amalgam of components mixed since pre-Holocean times. Though no differences have been found in uniparental and classical markers between Berbers and Arabs, the two main ethnic groups in the region, the scanty genomic data available have highlighted the singularity of Berbers. We characterize the genetic heterogeneity of North African groups, focusing on the putative differences of Berbers and Arabs, and estimate migration dates. We analyze genome-wide autosomal data in five Berber and six Arab groups, and compare them to Middle Easterns, sub-Saharans, and Europeans. Haplotype-based methods show a lack of correlation between geographical and genetic populations, and a high degree of genetic heterogeneity, without strong differences between Berbers and Arabs. Berbers enclose genetically diverse groups, from isolated endogamous groups with high autochthonous component frequencies, large homozygosity runs and low effective population sizes, to admixed groups with high frequencies of sub-Saharan and Middle Eastern components. Admixture time estimates show a complex pattern of recent historical migrations, with a peak around the 7th century C.E. coincident with the Arabization of the region; sub-Saharan migrations since the 1st century B.C. in agreement with Roman slave trade; and a strong migration in the 17th century C.E., coincident with a huge impact of the trans-Atlantic and trans-Saharan trade of sub-Saharan slaves in the Modern Era. The genetic complexity found should be taken into account when selecting reference groups in population genetics and biomedical studies.This work was supported by the Spanish MINECO grants CGL2013-44351-P and the “María de Maeztu” Program for Units of Excellence in R&D (MDM-2014-0370); and the Generalitat de Catalunya grant 2014SGR866