Abstract
Human forensic STRs used for individual identification have been reported to have little power for inter-population analyses. Several methods have been developed which incorporate information on the spatial distribution of individuals to arrive at a description of the arrangement of diversity. We genotyped at 16 forensic STRs a large population sample obtained from many locations in Italy, Greece and Turkey, i.e. three countries crucial to the understanding of discontinuities at the European/Asian junction and the genetic legacy of ancient migrations, but seldom represented together in previous studies. Using spatial PCA on the full dataset, we detected patterns of population affinities in the area. Additionally, we devised objective criteria to reduce the overall complexity into reduced datasets. Independent spatially explicit methods applied to these latter datasets converged in showing that the extraction of information on long- to medium-range geographical trends and structuring from the overall diversity is possible. All analyses returned the picture of a background clinal variation, with regional discontinuities captured by each of the reduced datasets. Several aspects of our results are confirmed on external STR datasets and replicate those of genome-wide SNP typings. High levels of gene flow were inferred within the main continental areas by coalescent simulations. These results are promising from a microevolutionary perspective, in view of the fast pace at which forensic data are being accumulated for many locales. It is foreseeable that this will allow the exploitation of an invaluable genotypic resource, assembled for other (forensic) purposes, to clarify important aspects in the formation of local gene pools.
Highlights
The power of forensic STR loci for individual identification has led to the accumulation of huge amounts of data, whose interest goes beyond forensic issues and potentially relates to the gene geography of human populations and microevolutionary processes
It was shown that the widely used index Fst is mathematically constrained for loci with high heterozygosity, while statistics derived from multivariate methods are able to extract ancestry information, reviving the value of loci for individual identification in population identifiability, at least at the continental scale [8]
The results reported here call for a replication of the analytical procedures on additional forensic STR datasets, in order to test their performance against known features of the gene geography of Europe and other areas [52]
Summary
The power of forensic STR loci for individual identification has led to the accumulation of huge amounts of data, whose interest goes beyond forensic issues and potentially relates to the gene geography of human populations and microevolutionary processes. Surveys of population samples with large arrays of STR loci [1, 2] have shown the ability of these markers to reveal many aspects of genetic structure in diverse human populations at the continental and sub-continental scales. Silva et al [6] detected a progressive reduction of diversity with increasing distance from Eastern Africa, a signature of the serial founder effect which accompanied the spread of modern humans out of Africa and beyond These latter authors found low fixation indices, and suggested that, as far as these markers have been selected to maximize the within-population (or between-subjects) variance, they carry a tiny proportion of information useful for between-population inferences. It was shown that the widely used index Fst is mathematically constrained for loci with high heterozygosity, while statistics derived from multivariate methods are able to extract ancestry information, reviving the value of loci for individual identification in population identifiability, at least at the continental scale [8]
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