Understanding the genomic heterogeneity of North African Imazighen: from broad to microgeographical perspectives.

The strategic location of North Africa has led to cultural and demographic shifts, shaping its genetic structure. Historical migrations brought different genetic components that are evident in present-day North African genomes, along with autochthonous components. The Imazighen (plural of Amazigh) are believed to be the descendants of autochthonous North Africans and speak various Amazigh languages, which belong to the Afro-Asiatic language family. However, the arrival of different human groups, especially during the Arab conquest, caused cultural and linguistic changes in local populations, increasing their heterogeneity. We aim to characterize the genetic structure of the region, using the largest Amazigh dataset to date and other reference samples. Our findings indicate microgeographical genetic heterogeneity among Amazigh populations, modeled by various admixture waves and different effective population sizes. A first admixture wave is detected group-wide around the twelfth century, whereas a second wave appears in some Amazigh groups around the nineteenth century. These events involved populations with higher genetic ancestry from south of the Sahara compared to the current North Africans. A plausible explanation would be the historical trans-Saharan slave trade, which lasted from the Roman times to the nineteenth century. Furthermore, our investigation shows that assortative mating in North Africa has been rare.

The Impact of Recent Demography on Functional Genetic Variation in North African Human Groups.

The strategic location of North Africa has made the region the core of a wide range of human demographic events, including migrations, bottlenecks, and admixture processes. This has led to a complex and heterogeneous genetic and cultural landscape, which remains poorly studied compared to other world regions. Whole-exome sequencing is particularly relevant to determine the effects of these demographic events on current-day North Africans' genomes, since it allows to focus on those parts of the genome that are more likely to have direct biomedical consequences. Whole-exome sequencing can also be used to assess the effect of recent demography in functional genetic variation and the efficacy of natural selection, a long-lasting debate. In the present work, we use newly generated whole-exome sequencing and genome-wide array genotypes to investigate the effect of demography in functional variation in 7 North African populations, considering both cultural and demographic differences and with a special focus on Amazigh (plur. Imazighen) groups. We detect genetic differences among populations related to their degree of isolation and the presence of bottlenecks in their recent history. We find differences in the functional part of the genome that suggest a relaxation of purifying selection in the more isolated groups, allowing for an increase of putatively damaging variation. Our results also show a shift in mutational load coinciding with major demographic events in the region and reveal differences within and between cultural and geographic groups.

Population analysis of complete mitogenomes for 334 samples from El Salvador.

The use of mitochondrial DNA (mtDNA) in the field of forensic genetics is widely spread mainly due to its advantages when identifying highly degraded samples. In this sense, massive parallel sequencing has made the analysis of the whole mitogenome more accessible, noticeably increasing the informativeness of mtDNA haplotypes. The civil war (1980-1992) in El Salvador caused many deaths and disappearances (including children) all across the country and the economic and social instability after the war forced many people to emigration. For this reason, different organizations have collected DNA samples from relatives with the aim of identifying missing people. Thus, we present a dataset containing 334 complete mitogenomes from the Salvadoran general population. To the best of our knowledge, this is the first publication of a nationwide forensic-quality complete mitogenome database of any Latin American country. We found 293 different haplotypes, with a random match probability of 0.0041 and 26.6 mean pairwise differences, which is similar to other Latin American populations, and which represent a marked improvement from the values obtained with just control region sequences. These haplotypes belong to 54 different haplogroups, being 91% of them of Native American origin. Over a third (35.9%) of the individuals carried at least a heteroplasmic site (excluding length heteroplasmies). Ultimately, the present database aims to represent mtDNA haplotype diversity in the general Salvadoran populations as a basis for the identification of people that disappeared during or after the civil war.

Whole mitogenomes reveal that NW Africa has acted both as a source and a destination for multiple human movements.

Despite being enclosed between the Mediterranean Sea and the Sahara Desert, North Africa has been the scenario of multiple human migrations that have shaped the genetic structure of its present-day populations. Despite its richness, North Africa remains underrepresented in genomic studies. To overcome this, we have sequenced and analyzed 264 mitogenomes from the Algerian Chaoui-speaking Imazighen (a.k.a. Berbers) living in the Aurès region. The maternal genetic composition of the Aurès is similar to Arab populations in the region, dominated by West Eurasian lineages with a moderate presence of M1/U6 North African and L sub-Saharan lineages. When focusing on the time and geographic origin of the North African specific clades within the non-autochthonous haplogroups, different geographical neighboring regions contributed to the North African maternal gene pool during time periods that could be attributed to previously suggested admixture events in the region, since Paleolithic times to recent historical movements such as the Arabization. We have also observed the role of North Africa as a source of geneflow mainly in Southern European regions since Neolithic times. Finally, the present work constitutes an effort to increase the representation of North African populations in genetic databases, which is key to understand their history.

Population history modulates the fitness effects of Copy Number Variation in the Roma.

We provide the first whole genome Copy Number Variant (CNV) study addressing Roma, along with reference populations from South Asia, the Middle East and Europe. Using CNV calling software for short-read sequence data, we identified 3171 deletions and 489 duplications. Taking into account the known population history of the Roma, as inferred from whole genome nucleotide variation, we could discern how this history has shaped CNV variation. As expected, patterns of deletion variation, but not duplication, in the Roma followed those obtained from single nucleotide polymorphisms (SNPs). Reduced effective population size resulting in slightly relaxed natural selection may explain our observation of an increase in intronic (but not exonic) deletions within Loss of Function (LoF)-intolerant genes. Over-representation analysis for LoF-intolerant gene sets hosting intronic deletions highlights a substantial accumulation of shared biological processes in Roma, intriguingly related to signaling, nervous system and development features, which may be related to the known profile of private disease in the population. Finally, we show the link between deletions and known trait-related SNPs reported in the genome-wide association study (GWAS) catalog, which exhibited even frequency distributions among the studied populations. This suggests that, in general human populations, the strong association between deletions and SNPs associated to biomedical conditions and traits could be widespread across continental populations, reflecting a common background of potentially disease/trait-related CNVs.

Y-chromosome target enrichment reveals rapid expansion of haplogroup R1b-DF27 in Iberia during the Bronze Age transition.

The Y chromosome can yield a unique perspective into the study of human demographic history. However, due to the repetitive nature of part of its sequence, only a small set of regions are suitable for variant calling and discovery from short-read sequencing data. These regions combined represent 8.9 Mbp or 0.14% of a diploid human genome. Consequently, investing in whole-genome sequencing to resolve Y-chromosome questions is poorly efficient. Here we use, as an alternative, target enrichment technology to greatly increase sequencing effectiveness, validating and applying the technique to 181 males, for 162 of whom we obtained a positive result. Additionally, 75 samples sequenced for the whole genome were also included, for a total sample size of 237. These samples were chosen for their Y chromosome haplogroup: R1b-DF27. In the context of European populations, and particularly in Iberia, this haplogroup stands out for its high frequency and its demographic history. Current evidence indicates that the diffusion of this haplogroup is related to the population movements that mark the cultural Bronze Age transition, making it remarkably interesting for population geneticists. The results of this study show the effects of the rapid radiation of the haplogroup in Spain, as even with the higher discriminating power of whole sequences, most haplotypes still fall within the R1b-DF27* paragroup rather than in the main derived branches. However, we were able to refine the ISOGG 2019-2020 phylogeny, and its two main subbranches, namely L176.2 and Z272, which present geographical differentiation between the Atlantic and Mediterranean coasts of Iberia.

Founder lineages in the Iberian Roma mitogenomes recapitulate the Roma diaspora and show the effects of demographic bottlenecks.

The Roma are the largest ethnic minority in Europe. With a Northwestern Indian origin around ~ 1.5 kya, they travelled throughout West Asia until their arrival in Europe around the eleventh century CE. Their diaspora through Europe is characterized by population bottlenecks and founder events which have contributed to their present day genetic and cultural diversity. In our study, we focus on the effects of founder effects in the mitochondrial DNA (mtDNA) pool of Iberian Roma by producing and analyzing 144 novel whole mtDNA sequences of Iberian Roma. Over 60% of their mtDNA pool is composed by founder lineages of South Asian origin or acquired by gene flow during their diaspora in the Middle East or locally in Europe in Europe. The TMRCA of these lineages predates the historical record of the Roma arrival in Spain. The abundance of founder lineages is in contrast with ~ 0.7% of autochthonous founder lineages present in the non-Roma Iberian population. Within those founder lineages, we found a substantial amount of South Asian M5a1b1a1 haplotypes and high frequencies of West Eurasian founder lineages (U3b1c, J2b1c, J1c1b, J1b3a, H88, among others), which we characterized phylogenetically and put in phylogeographical context. Besides, we found no evidence of genetic substructure of Roma within the Iberian Peninsula. These results show the magnitude of founder effects in the Iberian Roma and further explain the Roma history and genetic diversity from a matrilineal point of view.

Population Genetics of the European Roma-A Review.

The Roma are a group of populations with a common origin that share the Romani identity and cultural heritage. Their genetic history has been inferred through multiple studies based on uniparental and autosomal markers, and current genomic data have provided novel insights into their genetic background. This review was prompted by two factors: (i) new developments to estimate the genetic structure of the Roma at a fine-scale resolution have precisely identified the ancestral components and traced migrations that were previously documented only in historical sources, clarifying and solving debates on the origins and the diaspora of the Roma; (ii) while there has been an effort to review the health determinants of the Roma, the increasing literature on their population genetics has not been subjected to a dedicated review in the last two decades. We believe that a summary on the state of the art will benefit both the public and scholars that are approaching the subject.

Sequence diversity of the uniparentally transmitted portions of the genome in the resident population of Catalonia.

Genomic reference databases of residing populations are available in different countries and regions. Since they represent the whole genetic diversity of a geographical region, they have wide applications, from biomedical studies to forensic identifications. Uniparentally transmitted portions of the genome specifically are highly suitable for kinship analyses, mixed DNA cases and geographical ancestry inferences. We have sampled 808 individuals currently residing in Catalonia within the GCAT cohort, from which we have generated 808 high-quality whole mitochondrial DNA (mtDNA) genomes and 399 sequences of the male-specific part of the Y chromosome (MSY). We observe higher genetic diversity than in classical population genetics datasets. We test the robustness of whole sequences for unequivocal identifications, and we found that they have higher resolution than mitochondrial control region and Y chromosome short tandem repeats (Y-STRs), and that most of the variants they present are at low frequencies, increasing the discrimination capacity between individuals. These results confirm the forensic applicability of whole uniparental sequences and provide one of the largest high-quality reference datasets ever published.

Characterization of 58 STRs and 94 SNPs with the ForenSeq™ DNA signature prep kit in Mexican-Mestizos from the Monterrey city (Northeast, Mexico).

BACKGROUND: STR allele frequency databases from populations are necessary to take full advantage of the increased power of discrimination offered by massively parallel sequencing (MPS) platforms. MATERIAL AND METHODS: For this reason, we sequenced 58 STRs (aSTRs, X-STRs, and Y-STRs) and 94 identity informative SNPs (iiSNPs) on 105 Mestizo (admixed) individuals from Monterrey City (Northeast, Mexico), with the Primer Set-A of the ForenSeq™ DNA Signature Prep Kit. RESULTS: Most of the STR markers were in Hardy Weinberg equilibrium, with a few exceptions. We found 346 different length-based alleles for these 58 STRs; nevertheless, they became 528 alleles when the sequence was assessed. The combined power of discrimination from autosomal STRs (aSTRs) was -virtually- 100% in both length and sequence-based alleles, while the power of exclusion was 99.9999999976065 and 99.9999999999494%, respectively. Haplotypes based on X-STRs and Y-STRs showed 100% of discriminatory capacity. CONCLUSIONS: These results provide -for the first time- forensic genomic population data from Mexico necessary for interpretation in kinship and criminal analyses.

Risk-taking coping style correlates with SERT SNP290 polymorphisms in free-living great tits.

The coping style of an individual in relation to potentially dangerous situations has been suggested to be inherited in a polygenic fashion, SERT being one of the candidate genes. In this study, we assessed in free-living great tits (Parus major) the association between SNP290 in the SERT promoter and three standard fear-related behaviors: the response of the birds to a black-and-white flag fixed to the top of the nest box, distress calling rate of the birds in the hand once captured and the hissing call of incubating females when approached by a predator. We found a strong association between SNP290 polymorphism and the three risk-taking behaviors, with birds with genotype CT entering the nest box with the flag faster and displaying more distress calls and fewer hissing calls. CT birds could therefore be described as more proactive than CC individuals. These results also suggest that hissing behavior should be regarded as a fear-induced shy behavior, and confirm that SERT has an important function in relation to risk aversion behaviors and coping style.

A forensic population database in El Salvador: 58 STRs and 94 SNPs.

We have genotyped the 58 STRs (27 autosomal, 24 Y-STRs and 7 X-STRs) and 94 autosomal SNPs in Illumina ForenSeq™ Primer Mix A in a sample of 248 men and 143 women from El Salvador, Central America. Regional division (Centro, Oriente, Occidente) showed in almost all cases FST values not significantly different from 0, and further analyses were applied only to the undivided, country-wide population. The overall random match probability (RMP) decreased from 6.79 × 10-31 in length-based genotypes in the 27 autosomal STRs to 1.47 × 10-34 in repeat-sequence based genotypes. Combining the autosomal loci in this set, RMP reaches 2.97 × 10-70. In a population genetic analysis, El Salvador showed the lowest FST values with US Hispanics both for autosomal and X-STRs; however, it was much closer to Native Americans for the latter than for the former, in accordance with the well-known gender-biased admixture that created most Latin American populations.

Whole-exome analysis in Tunisian Imazighen and Arabs shows the impact of demography in functional variation.

Human populations are genetically affected by their demographic history, which shapes the distribution of their functional genomic variation. However, the genetic impact of recent demography is debated. This issue has been studied in different populations, but never in North Africans, despite their relevant cultural and demographic diversity. In this study we address the question by analyzing new whole-exome sequences from two culturally different Tunisian populations, an isolated Amazigh population and a close non-isolated Arab-speaking population, focusing on the distribution of functional variation. Both populations present clear differences in their variant frequency distribution, in general and for putatively damaging variation. This suggests a relevant effect in the Amazigh population of genetic isolation, drift, and inbreeding, pointing to relaxed purifying selection. We also discover the enrichment in Imazighen of variation associated to specific diseases or phenotypic traits, but the scarce genetic and biomedical data in the region limits further interpretation. Our results show the genomic impact of recent demography and reveal a clear genetic differentiation probably related to culture. These findings highlight the importance of considering cultural and demographic heterogeneity within North Africa when defining population groups, and the need for more data to improve knowledge on the region's health and disease landscape.

Admixture Has Shaped Romani Genetic Diversity in Clinically Relevant Variants.

Genetic patterns of inter-population variation are a result of different demographic and adaptive histories, which gradually shape the frequency distribution of the variants. However, the study of clinically relevant mutations has a Eurocentric bias. The Romani, the largest transnational minority ethnic group in Europe, originated in South Asia and received extensive gene flow from West Eurasia. Most medical genetic studies have only explored founder mutations related to Mendelian disorders in this population. Here we analyze exome sequences and genome-wide array data of 89 healthy Spanish Roma individuals to study complex traits and disease. We apply a different framework and focus on variants with both increased and decreased allele frequencies, taking into account their local ancestry. We report several OMIM traits enriched for genes with deleterious variants showing increased frequencies in Roma or in non-Roma (e.g., obesity is enriched in Roma, with an associated variant linked to South Asian ancestry; while non-insulin dependent diabetes is enriched in non-Roma Europeans). In addition, previously reported pathogenic variants also show differences among populations, where some variants segregating at low frequency in non-Roma are virtually absent in the Roma. Lastly, we describe frequency changes in drug-response variation, where many of the variants increased in Roma are clinically associated with metabolic and cardiovascular-related drugs. These results suggest that clinically relevant variation in Roma cannot only be characterized in terms of founder mutations. Instead, we observe frequency differences compared to non-Roma: some variants are absent, while other have drifted to higher frequencies. As a result of the admixture events, these clinically damaging variants can be traced back to both European and South Asian-related ancestries. This can be attributed to a different prevalence of some genetic disorders or to the fact that genetic susceptibility variants are mostly studied in populations of European descent, and can differ in individuals with different ancestries.

Second GHEP-ISFG exercise for DVI: "DNA-led" victims' identification in a simulated air crash.

The Spanish and Portuguese-Speaking Working Group of the International Society for Forensic Genetics (GHEP-ISFG) has organized a second collaborative exercise on a simulated case of Disaster Victim Identification (DVI), with the participation of eighteen laboratories. The exercise focused on the analysis of a simulated plane crash case of medium-size resulting in 66 victims with varying degrees of fragmentation of the bodies (with commingled remains). As an additional difficulty, this second exercise included 21 related victims belonging to 6 families among the 66 missings to be identified. A total number of 228 post-mortem samples were represented with aSTR and mtDNA profiles, with a proportion of partial aSTR profiles simulating charred remains. To perform the exercise, participants were provided with aSTR and mtDNA data of 51 reference pedigrees -some of which deficient-including 128 donors for identification purposes. The exercise consisted firstly in the comparison of the post-mortem genetic profiles in order to re-associate fragmented remains to the same individual and secondly in the identification of the re-associated remains by comparing aSTR and mtDNA profiles with reference pedigrees using pre-established thresholds to report a positive identification. Regarding the results of the post-mortem samples re-associations, only a small number of discrepancies among participants were detected, all of which were from just a few labs. However, in the identification process by kinship analysis with family references, there were more discrepancies in comparison to the correct results. The identification results of single victims yielded fewer problems than the identification of multiple related victims within the same family groups. Several reasons for the discrepant results were detected: a) the identity/non-identity hypotheses were sometimes wrongly expressed in the likelihood ratio calculations, b) some laboratories failed to use all family references to report the DNA match, c) In families with several related victims, some laboratories firstly identified some victims and then unnecessarily used their genetic information to identify the remaining victims within the family, d) some laboratories did not correctly use "prior odds" values for the Bayesian treatment of the episode for both post-mortem/post-mortem re-associations as well as the ante-mortem/post-mortem comparisons to evaluate the probability of identity. For some of the above reasons, certain laboratories failed to identify some victims. This simulated "DNA-led" identification exercise may help forensic genetic laboratories to gain experience and expertize for DVI or MPI in using genetic data and comparing their own results with the ones in this collaborative exercise.

The Counteracting Effects of Demography on Functional Genomic Variation: The Roma Paradigm.

Demographic history plays a major role in shaping the distribution of genomic variation. Yet the interaction between different demographic forces and their effects in the genomes is not fully resolved in human populations. Here, we focus on the Roma population, the largest transnational ethnic minority in Europe. They have a South Asian origin and their demographic history is characterized by recent dispersals, multiple founder events, and extensive gene flow from non-Roma groups. Through the analyses of new high-coverage whole exome sequences and genome-wide array data for 89 Iberian Roma individuals together with forward simulations, we show that founder effects have reduced their genetic diversity and proportion of rare variants, gene flow has counteracted the increase in mutational load, runs of homozygosity show ancestry-specific patterns of accumulation of deleterious homozygotes, and selection signals primarily derive from preadmixture adaptation in the Roma population sources. The present study shows how two demographic forces, bottlenecks and admixture, act in opposite directions and have long-term balancing effects on the Roma genomes. Understanding how demography and gene flow shape the genome of an admixed population provides an opportunity to elucidate how genomic variation is modeled in human populations.

Genetic origins, singularity, and heterogeneity of Basques.

Basques have historically lived along the Western Pyrenees, in the Franco-Cantabrian region, straddling the current Spanish and French territories. Over the last decades, they have been the focus of intense research due to their singular cultural and biological traits that, with high controversy, placed them as a heterogeneous, isolated, and unique population. Their non-Indo-European language, Euskara, is thought to be a major factor shaping the genetic landscape of the Basques. Yet there is still a lively debate about their history and assumed singularity due to the limitations of previous studies. Here, we analyze genome-wide data of Basque and surrounding groups that do not speak Euskara at a micro-geographical level. A total of ∼629,000 genome-wide variants were analyzed in 1,970 modern and ancient samples, including 190 new individuals from 18 sampling locations in the Basque area. For the first time, local- and wide-scale analyses from genome-wide data have been performed covering the whole Franco-Cantabrian region, combining allele frequency and haplotype-based methods. Our results show a clear differentiation of Basques from the surrounding populations, with the non-Euskara-speaking Franco-Cantabrians located in an intermediate position. Moreover, a sharp genetic heterogeneity within Basques is observed with significant correlation with geography. Finally, the detected Basque differentiation cannot be attributed to an external origin compared to other Iberian and surrounding populations. Instead, we show that such differentiation results from genetic continuity since the Iron Age, characterized by periods of isolation and lack of recent gene flow that might have been reinforced by the language barrier.

Autosomal genetics and Y-chromosome haplogroup L1b-M317 reveal Mount Lebanon Maronites as a persistently non-emigrating population.

Currently, there are 18 different religious communities living in Lebanon. While evolving primarily within Lebanon, these communities show a level of local isolation as demonstrated previously from their Y-haplogroup distributions. In order to trace the origins and migratory patterns that may have led to the genetic isolation and autosomal clustering in some of these communities we analyzed Y-chromosome STR and SNP sample data from 6327 individuals, in addition to whole genome autosomal sample data from 609 individuals, from Mount Lebanon and other surrounding communities. We observed Y chromosome L1b Levantine STR branching that occurred around 5000 years ago. Autosomal DNA analyses suggest that the North Lebanese Mountain Maronite community possesses an ancestral Fertile Crescent genetic component distinct from other populations in the region. We suggest that the Levantine L1b group split from the Caucasus ancestral group around 7300 years ago and migrated to the Levant. This event was distinct from the earlier expansions from the Caucasus region that contributed to the wider Levantine populations. Differential cultural adaption by populations from the North Lebanese Mountains are clearly aligned with the L1b haplotype STR haplogroup clusters, indicating pre-existing and persistent cultural barriers marked by the transmission of L1b lineages. Our findings highlight the value of uniparental haplogroups and STR haplotype data for elucidating biosocial events among these populations.

Recent Common Origin, Reduced Population Size, and Marked Admixture Have Shaped European Roma Genomes.

The Roma Diaspora-traditionally known as Gypsies-remains among the least explored population migratory events in historical times. It involved the migration of Roma ancestors out-of-India through the plateaus of Western Asia ultimately reaching Europe. The demographic effects of the Diaspora-bottlenecks, endogamy, and gene flow-might have left marked molecular traces in the Roma genomes. Here, we analyze the whole-genome sequence of 46 Roma individuals pertaining to four migrant groups in six European countries. Our analyses revealed a strong, early founder effect followed by a drastic reduction of ∼44% in effective population size. The Roma common ancestors split from the Punjabi population, from Northwest India, some generations before the Diaspora started, <2,000 years ago. The initial bottleneck and subsequent endogamy are revealed by the occurrence of extensive runs of homozygosity and identity-by-descent segments in all Roma populations. Furthermore, we provide evidence of gene flow from Armenian and Anatolian groups in present-day Roma, although the primary contribution to Roma gene pool comes from non-Roma Europeans, which accounts for >50% of their genomes. The linguistic and historical differentiation of Roma in migrant groups is confirmed by the differential proportion, but not a differential source, of European admixture in the Roma groups, which shows a westward cline. In the present study, we found that despite the strong admixture Roma had in their diaspora, the signature of the initial bottleneck and the subsequent endogamy is still present in Roma genomes.