Human Genomic Diversity Where the Mediterranean Joins the Atlantic.

Throughout the past few years, a lively debate emerged about the timing and magnitude of the human migrations between the Iberian Peninsula and the Maghreb. Several pieces of evidence, including archaeological, anthropological, historical, and genetic data, have pointed to a complex and intermingled evolutionary history in the western Mediterranean area. To study to what extent connections across the Strait of Gibraltar and surrounding areas have shaped the present-day genomic diversity of its populations, we have performed a screening of 2.5 million single-nucleotide polymorphisms in 142 samples from southern Spain, southern Portugal, and Morocco. We built comprehensive data sets of the studied area and we implemented multistep bioinformatic approaches to assess population structure, demographic histories, and admixture dynamics. Both local and global ancestry inference showed an internal substructure in the Iberian Peninsula, mainly linked to a differential African ancestry. Western Iberia, from southern Portugal to Galicia, constituted an independent cluster within Iberia characterized by an enriched African genomic input. Migration time modeling showed recent historic dates for the admixture events occurring both in Iberia and in the North of Africa. However, an integrative vision of both paleogenomic and modern DNA data allowed us to detect chronological transitions and population turnovers that could be the result of transcontinental migrations dating back from Neolithic times. The present contribution aimed to fill the gaps in the modern human genomic record of a key geographic area, where the Mediterranean and the Atlantic come together.

Genetic variation patterns of ß-thalassemia in Western Andalusia (Spain) reveal a structure of specific mutations within the Iberian Peninsula.

BACKGROUND: Analyses of the genomic variation in the western Mediterranean population are being used to reveal its evolutionary history and to understand the molecular basis of particular diseases. AIM: To observe the ß-thalassemia mutational spectrum in western Andalusia, Spain, in the context of the Mediterranean. In addition, associations between disease and neutral gene variants within the ß-globin gene (HBB) were also evaluated. SUBJECTS AND METHODS: This study included 63 unrelated individuals diagnosed with ß-thalassemia. In addition, 97 unrelated, healthy subjects of the same territory were also analysed as proxies of the normal genetic background. Allele associations and population genetic structure analyses were performed using different methodologies. RESULTS: Data have revealed a rather restricted spectrum of ß-thalassemia mutations in the analysed sample. Although the detected variants fit well with the Mediterranean pattern, certain singularities support a structure of some specific ß-thalassemia alleles. The IVSI-1 (G > A) shows a strong regionalisation. The spatial correlogram revealed a typically narrow wave structure, presumably linked to genetic isolation and genetic drift. CONCLUSIONS: The long history of endemic malaria in the study territory, the rather high consanguinity rates among its autochthonous population, and other demographic features have been used here to understand the western Andalusian ß-thalassemia molecular portrait.

Paternal lineages in southern Iberia provide time frames for gene flow from mainland Europe and the Mediterranean world.

BACKGROUND: The geography of southern Iberia and an abundant archaeological record of human occupation are ideal conditions for a full understanding of scenarios of genetic history in the area. Recent advances in the phylogeography of Y-chromosome lineages offer the opportunity to set upper bounds for the appearance of different genetic components. AIM: To provide a global knowledge on the Y haplogroups observed in Andalusia with their Y microsatellite variation. Preferential attention is given to the vehement debate about the age, origin and expansion of R1b-M269 clade and sub-lineages. SUBJECT AND METHODS: Four hundred and fourteen male DNA samples from western and eastern autochthonous Andalusians were genotyped for a set of Y-SNPs and Y-STRs. Gene diversity, potential population genetic structures and coalescent times were assessed. RESULTS: Most of the analysed samples belong to the European haplogroup R1b1a1a2-M269, whereas haplogroups E, J, I, G and T show lower frequencies. A phylogenetic dissection of the R1b-M269 was performed and younger time frames than those previously reported in the literature were obtained for its sub-lineages. CONCLUSION: The particular Andalusian R1b-M269 assemblage confirms the shallow topology of the clade. Moreover, the sharing of lineages with the rest of Europe indicates the impact in Iberia of an amount of pre-existing diversity, with the possible exception of R1b-DF27. Lineages such as J2-M172 and G-M201 highlight the importance of maritime travels of early farmers who reached the Iberian Peninsula.

The distribution of mitochondrial DNA haplogroup H in southern Iberia indicates ancient human genetic exchanges along the western edge of the Mediterranean.

BACKGROUND: The structure of haplogroup H reveals significant differences between the western and eastern edges of the Mediterranean, as well as between the northern and southern regions. Human populations along the westernmost Mediterranean coasts, which were settled by individuals from two continents separated by a relatively narrow body of water, show the highest frequencies of mitochondrial haplogroup H. These characteristics permit the analysis of ancient migrations between both shores, which may have occurred via primitive sea crafts and early seafaring. We collected a sample of 750 autochthonous people from the southern Iberian Peninsula (Andalusians from Huelva and Granada provinces). We performed a high-resolution analysis of haplogroup H by control region sequencing and coding SNP screening of the 337 individuals harboring this maternal marker. Our results were compared with those of a wide panel of populations, including individuals from Iberia, the Maghreb, and other regions around the Mediterranean, collected from the literature. RESULTS: Both Andalusian subpopulations showed a typical western European profile for the internal composition of clade H, but eastern Andalusians from Granada also revealed interesting traces from the eastern Mediterranean. The basal nodes of the most frequent H sub-haplogroups, H1 and H3, harbored many individuals of Iberian and Maghrebian origins. Derived haplotypes were found in both regions; haplotypes were shared far more frequently between Andalusia and Morocco than between Andalusia and the rest of the Maghreb. These and previous results indicate intense, ancient and sustained contact among populations on both sides of the Mediterranean. CONCLUSIONS: Our genetic data on mtDNA diversity, combined with corresponding archaeological similarities, provide support for arguments favoring prehistoric bonds with a genetic legacy traceable in extant populations. Furthermore, the results presented here indicate that the Strait of Gibraltar and the adjacent Alboran Sea, which have often been assumed to be an insurmountable geographic barrier in prehistory, served as a frequently traveled route between continents.

Matrilineal Heritage in Southern Iberia Reveals Deep Genetic Links between Continents.

Within the Mediterranean Basin, the Iberian Peninsula has been a focus of attraction for several cultures and civilizations from its prehistory and history, making it a target territory for studying human migration patterns and peopling processes using a wide and heterogeneous spectrum of genomic markers. While its Cantabrian fringe represents the most regularly analysed area in terms of its mitochondrial diversity, the absence of monographic surveys on the maternal genetic composition of southern Iberians (i.e., Andalusians) is striking. In this work, we present a comprehensive view of various aspects of the human maternal heritage of the autochthonous Andalusian population regarding specific mitochondrial haplogroups considered key candidates to determine the genetic relationship between Europe and Africa. Data reveal that southern Iberian populations do not have genetically homogeneous mitochondrial DNA profiles, and their observed genetic affinity with north-western African populations represents strong signals of old, sustained and bidirectional human movements between the northern and southern shores of the western Mediterranean. Thorough analyses of African mtDNA haplogroups have shown that the most relevant African contribution within Iberian Peninsula could be explained as a consequence of prehistoric events. The subsequent historic episodes helped to strengthen the ties between both shores. In southern Iberia, mitochondrial and other genetic markers show that the Strait of Gibraltar together with its surrounding maritime areas should be considered a bridge between continents. More broadly, the Mediterranean Sea has acted as a transport surface, that is, as a permeable barrier to human migrations from prehistoric and historic times. In conclusion, this research contributes to our knowledge of processes that have shaped the recent human genetic history in the Mediterranean and, more specifically, of the population dynamics that the inhabitants of southern Iberia have experienced with respect to other neighbouring North African populations.

Human maternal heritage in Andalusia (Spain): its composition reveals high internal complexity and distinctive influences of mtDNA haplogroups U6 and L in the western and eastern side of region.

BACKGROUND: The archeology and history of the ancient Mediterranean have shown that this sea has been a permeable obstacle to human migration. Multiple cultural exchanges around the Mediterranean have taken place with presumably population admixtures. A gravitational territory of those migrations has been the Iberian Peninsula. Here we present a comprehensive analysis of the maternal gene pool, by means of control region sequencing and PCR-RFLP typing, of autochthonous Andalusians originating from the coastal provinces of Huelva and Granada, located respectively in the west and the east of the region. RESULTS: The mtDNA haplogroup composition of these two southern Spanish populations has revealed a wide spectrum of haplogroups from different geographical origins. The registered frequencies of Eurasian markers, together with the high incidence and diversification of African maternal lineages (15% of the total mitochondrial variability) among Huelva Andalusians when compared to its eastwards relatives of Granada and other Iberian populations, constitute relevant findings unknown up-to-date on the characteristics of mtDNA within Andalusia that testifies a female population substructure. Therefore, Andalusia must not be considered a single, unique population. CONCLUSIONS: The maternal legacy among Andalusians reflects distinctive local histories, pointing out the role of the westernmost territory of Peninsular Spain as a noticeable recipient of multiple and diverse human migrations. The obtained results underline the necessity of further research on genetic relationships in both sides of the western Mediterranean, using carefully collected samples from autochthonous individuals. Many studies have focused on recent North African gene flow towards Iberia, yet scientific attention should be now directed to thoroughly study the introduction of European genes in northwest Africa across the sea, in order to determine its magnitude, timescale and methods, and to compare them to those terrestrial movements from eastern Africa and southwestern Asia.

New insights into the distribution of APOE polymorphism in the Iberian Peninsula. The case of Andalusia (Spain).

BACKGROUND: The APOE gene has received much attention due to the remarkable spatial variation patterns of some of its genotypes and alleles in human populations and to its relevance in biomedicine. AIM: This work was addressed to investigate the extent of APOE polymorphism between autochthonous Andalusians originating from Huelva and Granada provinces. No data on this marker in these southern Spanish coastal populations are available up to date. SUBJECTS AND METHODS: This study used genomic DNA from healthy, unrelated Andalusians of both sexes (n = 322). All samples were genotyped for two SNPs, rs429358 and rs7412, which determine the three APOE alleles: ε2, ε3 and ε4. For analyses, a TaqMan-based technique was applied using a RT-PCR. Comparisons with other Mediterranean populations were performed based on multivariate analysis. RESULTS: A relatively high frequency of ε4 in Granada (eastern Andalusia), as well as a low ε2 frequency in Huelva (western Andalusia) were observed. The finding that ε4 allele in Southern Spain and Portugal is higher than expected given its geographical location poses an interesting question for this study, given the well-established APOE-ε4 gradient in Europe. CONCLUSION: This population study may represent useful information for further prospective anthropological and molecular genetic studies focused on unravelling the relationship between population genetic composition and specific human diseases.

Mitochondrial DNA in Human Diversity and Health: From the Golden Age to the Omics Era.

Mitochondrial DNA (mtDNA) is a small fraction of our hereditary material. However, this molecule has had an overwhelming presence in scientific research for decades until the arrival of high-throughput studies. Several appealing properties justify the application of mtDNA to understand how human populations are-from a genetic perspective-and how individuals exhibit phenotypes of biomedical importance. Here, I review the basics of mitochondrial studies with a focus on the dawn of the field, analysis methods and the connection between two sides of mitochondrial genetics: anthropological and biomedical. The particularities of mtDNA, with respect to inheritance pattern, evolutionary rate and dependence on the nuclear genome, explain the challenges of associating mtDNA composition and diseases. Finally, I consider the relevance of this single locus in the context of omics research. The present work may serve as a tribute to a tool that has provided important insights into the past and present of humankind.

Surnames and Y-chromosomal markers reveal low relationships in Southern Spain.

A sample of 416 males from western and eastern Andalusia has been jointly analyzed for surnames and Y-chromosome haplogroups and haplotypes. The observed number of different surnames was 222 (353 when the second surname of the Spanish system of naming is considered). The great majority of recorded surnames have a Castilian-Leonese origin, while Catalan or Basque surnames have not been found. A few Arab-related surnames appear but none discernible of Sephardic-Jewish descent. Low correlation among surnames with different population frequencies and Y-chromosome markers, at different levels of genetic resolution, has been observed in Andalusia. This finding could be explained mainly by the very low rate of monophyletic surnames because of the historical process of surname ascription and the resulting high frequencies of the most common Spanish surnames. The introduction of surnames in Spain during the Middle Ages coincided with Reconquest of the territories under Islamic rule, and Muslims and Jews progressively adopted the present male line surname system. Sampled surnames and Y-chromosome lineages fit well a power-law distribution and observed isonymy is very close to that of the general population. Besides, our data and results show that the reliability of the isonymy method should be questioned because of the high rate of polyphyletic surnames, even in small geographic regions and autochthonous populations. Random isonymy would be consistently dependent of the most common surname frequencies in the population.

Early Holocenic and Historic mtDNA African Signatures in the Iberian Peninsula: The Andalusian Region as a Paradigm.

Determining the timing, identity and direction of migrations in the Mediterranean Basin, the role of "migratory routes" in and among regions of Africa, Europe and Asia, and the effects of sex-specific behaviors of population movements have important implications for our understanding of the present human genetic diversity. A crucial component of the Mediterranean world is its westernmost region. Clear features of transcontinental ancient contacts between North African and Iberian populations surrounding the maritime region of Gibraltar Strait have been identified from archeological data. The attempt to discern origin and dates of migration between close geographically related regions has been a challenge in the field of uniparental-based population genetics. Mitochondrial DNA (mtDNA) studies have been focused on surveying the H1, H3 and V lineages when trying to ascertain north-south migrations, and U6 and L in the opposite direction, assuming that those lineages are good proxies for the ancestry of each side of the Mediterranean. To this end, in the present work we have screened entire mtDNA sequences belonging to U6, M1 and L haplogroups in Andalusians--from Huelva and Granada provinces--and Moroccan Berbers. We present here pioneer data and interpretations on the role of NW Africa and the Iberian Peninsula regarding the time of origin, number of founders and expansion directions of these specific markers. The estimated entrance of the North African U6 lineages into Iberia at 10 ky correlates well with other L African clades, indicating that U6 and some L lineages moved together from Africa to Iberia in the Early Holocene. Still, founder analysis highlights that the high sharing of lineages between North Africa and Iberia results from a complex process continued through time, impairing simplistic interpretations. In particular, our work supports the existence of an ancient, frequently denied, bridge connecting the Maghreb and Andalusia.

Immunoglobulin genes in Andalusia (Spain). Genetic diversity in the Mediterranean space.

Andalusia is the most densely populated region of Spain since ancient times, and has a rich history of contacts across the Mediterranean. Earlier studies have underlined the relatively high frequency of the Sub-Saharan GM 1,17 5* haplotype in western Andalusia (Huelva province, n=252) and neighbouring Atlantic regions. Here, we provide novel data on GM/KM markers in eastern Andalusians (n=195) from Granada province, where African GM*1,17 5* frequency is relatively high (0.044). The most frequent GM haplotypes in Andalusia parallel the most common in Europe. Altogether, these data allow us to gain insight into the genetic diversity of southern Iberia. Additionally, we assess population structure by comparing our Iberian samples with 41 Mediterranean populations. GM haplotype variation across the Mediterranean reflects intense and complex interactions between North Africans and South Europeans along human history, highlighting that African influence over the Iberian Peninsula does not follow an isotropic pattern.