Abstract
The forensic genetics field is generating extensive population data on polymorphism of short tandem repeats (STR) markers in globally distributed samples. In this study we explored and quantified the informative power of these datasets to address issues related to human evolution and diversity, by using two online resources: an allele frequency dataset representing 141 populations summing up to almost 26 thousand individuals; a genotype dataset consisting of 42 populations and more than 11 thousand individuals. We show that the genetic relationships between populations based on forensic STRs are best explained by geography, as observed when analysing other worldwide datasets generated specifically to study human diversity. However, the global level of genetic differentiation between populations (as measured by a fixation index) is about half the value estimated with those other datasets, which contain a much higher number of markers but much less individuals. We suggest that the main factor explaining this difference is an ascertainment bias in forensics data resulting from the choice of markers for individual identification. We show that this choice results in average low variance of heterozygosity across world regions, and hence in low differentiation among populations. Thus, the forensic genetic markers currently produced for the purpose of individual assignment and identification allow the detection of the patterns of neutral genetic structure that characterize the human population but they do underestimate the levels of this genetic structure compared to the datasets of STRs (or other kinds of markers) generated specifically to study the diversity of human populations.
Highlights
Short Tandem Repeats (STRs) or microsatellites are popular genetic markers in many applications of genetics, from population characterisation to individual identification and they have been widely used for gene mapping [1]
In this study we present the results of analyses performed to describe the patterns and levels of genetic diversity and structure of human populations inferred from each of the two worldwide forensic datasets described above, i.e. the frequency distributions compiled in strdna-db and the genotype profiles assembled in PopAffiliator
In conclusion, we show that the two forensic datasets investigated contain valuable, albeit limited, information on worldwide genetic diversity, even after a careful selection of welldefined samples as explained in Materials and Methods
Summary
Short Tandem Repeats (STRs) or microsatellites are popular genetic markers in many applications of genetics, from population characterisation to individual identification and they have been widely used for gene mapping [1]. The popularity of STRs is due to their hypervariability and ubiquity throughout the genome [2], summing up to 150,000 informative loci with a guaranteed polymorphic level [3] The variability of these markers is a consequence of a high mutation rate [4], one of the fastest rates among commonly used genetic markers, at least four to six orders of magnitude higher than that of single nucleotide polymorphisms (SNP) [5,6]. The type of STRs (number of bases per repeat) was shown to influence the resulting population structure, and the geographic dispersion of the samples was claimed to be an important factor [14,15,16]
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