Angela
Elite member
- Messages
- 21,823
- Reaction score
- 12,328
- Points
- 113
- Ethnic group
- Italian
See:
Clare Bycroft1, Ceres Fernandez-Rozadilla2, Clara Ruiz-Ponte2, Inés Quintela-García2,3, Ángel Carracedo2,3, Peter Donnelly1,4†, Simon Myers4,1†‡
"Patterns of genetic differentiation and the footprints of historical migrations in the Iberian Peninsula"
https://www.biorxiv.org/content/biorxiv/early/2018/03/12/250191.full.pdf
"Genetic differences within or between human populations (population structure) has been studied using a variety of approaches over many years1-5. Recently there has been an increasing focus on studying genetic differentiation at fine geographic scales, such as within countries6-8. Identifying such structure allows the study of recent population history, and identifies the potential for confounding in association studies, particularly when testing rare, often recently arisen variants9. The Iberian Peninsula is linguistically diverse, has a complex demographic history, and is unique among European regions in having a centuries-long period of Muslim rule10.Previous genetic studies of Spain have examined either a small fraction of the genome12-14 or only a few Spanish regions15,16. Thus, the overall pattern of fine-scale population structure within Spain remains uncharacterised. Here we analysegenome-wide genotyping array data for 1,413 Spanish individuals sampled from all regions of Spain. We identify extensive fine-scale structure, down to unprecedented scales, smaller than 10 Km in some places. We observe a major axis of genetic differentiation that runs from east to west of the peninsula. In contrast, we observeremarkable genetic similarity in the north-south direction, and evidence of historical north-south population movement. Finally, without making particular prior assumptions about source populations, we show that modern Spanish people have regionally varying fractions of ancestry from a group most similar to modern north Moroccans. The north African ancestry results from an admixture event, which wedate to 860 - 1120 CE, corresponding to the early half of Muslim rule. Our results indicate that it is possible to discern clear genetic impacts of the Muslim conquest and population movements associated with the subsequent Reconquista."
They're using people with all four grandparents from the same region, so all the results are reflecting the clusters from around 1900, when there might have already been some modern internal migration.
"Overall, the major axis of genetic differentiation runs from east to west, while conversely there is remarkable genetic similarity on the north-south direction. In a complementary analysis that included Portugal, although fewer SNPs (Methods), Portuguese individuals co-clustered with individuals in Galicia (Supplementary Figure 1a), showing that this pattern extends across the whole Iberian Peninsula. Indeed, rather than solely reflecting modern-day political boundaries, the broad-scale genetic structure of the region is strikingly similar to the linguistic frontiers present in the Iberian Peninsula around 1300 CE (Figure 1c)."
I'm not so sure about part of the above. It seems to me that the north to south "general" similarity reflects the Reconquista.
"For all six Iberian clusters the largest contribution comes from France (63 - 91%), with smaller contributions that relate to present-day Italian (5 - 17%) and Irish (2 - 5%) groups. With the exception of the Basque cluster, these three donor groups dominate, and contributeproportionally similar amounts throughout Iberia, so probably represent ancient ancestry components rather than recent migration. In contrast, north Moroccan ancestry shows strong regional variation (Figure 3c, Methods). See Supplementary Information for a fuller discussion of the ancestry profiles."
"To distinguish between possible scenarios that could produce these patterns, we applied the GLOBETROTTER method20 to each of our six clusters (Methods). GLOBETROTTER infers dates of admixture and the make-up of the source populations, and tests whether admixture patterns are consistent with a simple mixing of two groups at a single time in the past, compared to more complex alternative models. GLOBETROTTER found strong evidence (p < 0.01) of admixture for all six clusters (Methods; Table S3a in Supplementary Information). For all six clusters, an extremely similar event was inferred (Figure 3b), in a tight time-range of 860 - 1120 CE, and with similar source groups, present in varying proportions (4 -10% for the minor group). The major source was inferred to contain almost exclusively European donor groups, and the minor source is made up of mainly north west African donor groups, including Western Sahara, and to a lesser extent west Africans (YRI), consistent with the overall ancestry profiles. The ‘Portugal-Andalucia’ cluster shows the greatest YRI contribution, and also shows some evidence of a second admixture date, with a more recent event involving only sub-SaharanAfrican-likeand European-like source groups (see Supplementary Information for a fuller discussion; Supplementary Figure 6). This indicates a recent pulse of subSaharanAfrican DNA, independent of the north African component."
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Clare Bycroft1, Ceres Fernandez-Rozadilla2, Clara Ruiz-Ponte2, Inés Quintela-García2,3, Ángel Carracedo2,3, Peter Donnelly1,4†, Simon Myers4,1†‡
"Patterns of genetic differentiation and the footprints of historical migrations in the Iberian Peninsula"
https://www.biorxiv.org/content/biorxiv/early/2018/03/12/250191.full.pdf
"Genetic differences within or between human populations (population structure) has been studied using a variety of approaches over many years1-5. Recently there has been an increasing focus on studying genetic differentiation at fine geographic scales, such as within countries6-8. Identifying such structure allows the study of recent population history, and identifies the potential for confounding in association studies, particularly when testing rare, often recently arisen variants9. The Iberian Peninsula is linguistically diverse, has a complex demographic history, and is unique among European regions in having a centuries-long period of Muslim rule10.Previous genetic studies of Spain have examined either a small fraction of the genome12-14 or only a few Spanish regions15,16. Thus, the overall pattern of fine-scale population structure within Spain remains uncharacterised. Here we analysegenome-wide genotyping array data for 1,413 Spanish individuals sampled from all regions of Spain. We identify extensive fine-scale structure, down to unprecedented scales, smaller than 10 Km in some places. We observe a major axis of genetic differentiation that runs from east to west of the peninsula. In contrast, we observeremarkable genetic similarity in the north-south direction, and evidence of historical north-south population movement. Finally, without making particular prior assumptions about source populations, we show that modern Spanish people have regionally varying fractions of ancestry from a group most similar to modern north Moroccans. The north African ancestry results from an admixture event, which wedate to 860 - 1120 CE, corresponding to the early half of Muslim rule. Our results indicate that it is possible to discern clear genetic impacts of the Muslim conquest and population movements associated with the subsequent Reconquista."
They're using people with all four grandparents from the same region, so all the results are reflecting the clusters from around 1900, when there might have already been some modern internal migration.
"Overall, the major axis of genetic differentiation runs from east to west, while conversely there is remarkable genetic similarity on the north-south direction. In a complementary analysis that included Portugal, although fewer SNPs (Methods), Portuguese individuals co-clustered with individuals in Galicia (Supplementary Figure 1a), showing that this pattern extends across the whole Iberian Peninsula. Indeed, rather than solely reflecting modern-day political boundaries, the broad-scale genetic structure of the region is strikingly similar to the linguistic frontiers present in the Iberian Peninsula around 1300 CE (Figure 1c)."
I'm not so sure about part of the above. It seems to me that the north to south "general" similarity reflects the Reconquista.
"For all six Iberian clusters the largest contribution comes from France (63 - 91%), with smaller contributions that relate to present-day Italian (5 - 17%) and Irish (2 - 5%) groups. With the exception of the Basque cluster, these three donor groups dominate, and contributeproportionally similar amounts throughout Iberia, so probably represent ancient ancestry components rather than recent migration. In contrast, north Moroccan ancestry shows strong regional variation (Figure 3c, Methods). See Supplementary Information for a fuller discussion of the ancestry profiles."
"To distinguish between possible scenarios that could produce these patterns, we applied the GLOBETROTTER method20 to each of our six clusters (Methods). GLOBETROTTER infers dates of admixture and the make-up of the source populations, and tests whether admixture patterns are consistent with a simple mixing of two groups at a single time in the past, compared to more complex alternative models. GLOBETROTTER found strong evidence (p < 0.01) of admixture for all six clusters (Methods; Table S3a in Supplementary Information). For all six clusters, an extremely similar event was inferred (Figure 3b), in a tight time-range of 860 - 1120 CE, and with similar source groups, present in varying proportions (4 -10% for the minor group). The major source was inferred to contain almost exclusively European donor groups, and the minor source is made up of mainly north west African donor groups, including Western Sahara, and to a lesser extent west Africans (YRI), consistent with the overall ancestry profiles. The ‘Portugal-Andalucia’ cluster shows the greatest YRI contribution, and also shows some evidence of a second admixture date, with a more recent event involving only sub-SaharanAfrican-likeand European-like source groups (see Supplementary Information for a fuller discussion; Supplementary Figure 6). This indicates a recent pulse of subSaharanAfrican DNA, independent of the north African component."
Also, the currents and winds in the Mediterranean flow in particular patterns so that travel between even two locales which are very close as the crow flies can be exceedingly difficult. It took very sophisticated navigation advances to counter that, and that happened much further on than the periods we're discussing. 
