Abstract
Human populations are often dichotomized into “isolated” and “open” categories using cultural and/or geographical barriers to gene flow as differential criteria. Although widespread, the use of these alternative categories could obscure further heterogeneity due to inter-population differences in effective size, growth rate, and timing or amount of gene flow. We compared intra and inter-population variation measures combining novel and literature data relative to 87,818 autosomal SNPs in 14 open populations and 10 geographic and/or linguistic European isolates. Patterns of intra-population diversity were found to vary considerably more among isolates, probably due to differential levels of drift and inbreeding. The relatively large effective size estimated for some population isolates challenges the generalized view that they originate from small founding groups. Principal component scores based on measures of intra-population variation of isolated and open populations were found to be distributed along a continuum, with an area of intersection between the two groups. Patterns of inter-population diversity were even closer, as we were able to detect some differences between population groups only for a few multidimensional scaling dimensions. Therefore, different lines of evidence suggest that dichotomizing human populations into open and isolated groups fails to capture the actual relations among their genomic features.
Highlights
By inter-population differences in effective size, growth rate and timing or extent of gene flow reduction
With the introduction of SNP microarrays, which enable the simultaneous analysis of hundreds of thousands of loci distributed across the genome, it is possible to investigate the genetic structure of human populations on a fine scale[10]
We can detect signatures of isolation which are not revealed by unilinear markers, such as the increase in the number and size of stretches of consecutive homozygous genotypes, shared chromosomal segments identical by descent (IBD) and Linkage Disequilibrium (LD)[2,3,11,12,13,14]
Summary
By inter-population differences in effective size, growth rate and timing or extent of gene flow reduction. The lack of recombination limits the power of these genetic systems in the detection of signatures of genetic isolation in different historical and demographic conditions. Relations between genomic differences and demographic or historical factors and their implications for the gene mapping of Mendelian or complex traits have been studied[1,2,3], while LD patterns have been compared in isolates distributed worldwide[14]. To the best of our knowledge, no study has systematically explored the structure of genomic diversity in isolated populations comparing them with a comprehensive set of open populations. We compare the distribution of intra- and inter-population measures of variation in isolated and open populations in order to understand to what extent the discrete open and isolated dichotomous categories correspond to the way in which their genomic diversity is structured
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