Gene flow from North Africa contributes to differential human genetic diversity in southern Europe

Abstract

Human genetic diversity in southern Europe is higher than in other regions of the continent. This difference has been attributed to postglacial expansions, the demic diffusion of agriculture from the Near East, and gene flow from Africa. Using SNP data from 2,099 individuals in 43 populations, we show that estimates of recent shared ancestry between Europe and Africa are substantially increased when gene flow from North Africans, rather than Sub-Saharan Africans, is considered. The gradient of North African ancestry accounts for previous observations of low levels of sharing with Sub-Saharan Africa and is independent of recent gene flow from the Near East. The source of genetic diversity in southern Europe has important biomedical implications; we find that most disease risk alleles from genome-wide association studies follow expected patterns of divergence between Europe and North Africa, with the principal exception of multiple sclerosis.

The Italian genome reflects the history of Europe and the Mediterranean basin

“…According to previous studies on the Y chromosome and mtDNA, 34,35 the Middle Eastern ancestry in Southern Italians most likely originated at the time of the Greek colonization and, with a smaller percentage, of the subsequent Arabic domination, 7 whereas in Central-Northern Italy it is possibly because of the admixture of the indigenous residents with Middle Eastern populations spreading from the Caucasus to Central Europe. 19,21,28,36 Our results agree with previously published reports describing a possible maritime route of colonization across Europe, including Italy, 37 although we cannot exclude the occurrence of more recent demographic events leading to a similar scenario. Finally, the homogenous ancestral effective population size across Italian regions could be interpreted as reflecting common genetic origins, taking also into account previous considerations, although the same results might also occur in comparing populations without common origins.…”

“…The statistics W AB defined by Atzmon et al 20 and L AB defined by Botigue et al 21 were computed as a summary of IBD sharing. The first is an index of the total length of the shared IBD blocks averaged over the number of possible pairs of individuals (one from population A and the other from population B); the second is an index of the average length of a segment shared IBD between a pair of individuals normalized over the possible number of pairwise …”

Demographic Events and Evolutionary Forces Shaping European Genetic Diversity

“…In our article, we argued that admixture across the Mediterranean certainly contributes to the N/S pattern ( process d), and more extensive work by others supports this hypothesis (Botigué et al 2013). To what extent this admixture is layered on top of other patterns (caused by processes a, b, c, and e listed above) is still a very open question and shows the challenges of interpreting the results of a palimpsest pattern of genetic variation.…”

Ancient genomes link early farmers from Atapuerca in Spain to modern-day Basques

“…All modern-day Iberian groups displayed ancestry from early farmers and hunter-gatherers and also showed admixture from North Africa (Fig. 3A, yellow component) (23) and the Caucasus/ Central Asia (Fig. 3A, dark purple component), potentially related to the observed migration during the Bronze Age (24,25) or the later Roman Empire ruling of Iberia.…”