Finnish population genetics in a forensic context

The singularity of population structure observed in Finland is the ultimate result of a number of factors in history. Finland’s late emergence from the Pleistocene era coupled with its geographical isolation, low initial density of the breeding population and limited gene flow have ultimately contributed to genetic dissociation from the rest of Europe, post-expansion amplification of distinctive genes, and the retention of a homogenous character. This unusual history and resulting structure have a number of consequences for the practical applications of genetic testing in Finland today, including forensic analysis. The objective of this study was to characterize coding and noncoding genetic variation in the Finnish gene pool using forensic markers, in order to improve the efficiency of forensic testing in Finland while simultaneously broadening our understanding of its history. Finland is characterized by a clear genetic delineation between Eastern and Western regions of the country. The origins of this substructure in different marker classes have heretofore remained undetermined. Here, patterns of distribution observed in markers of prehistoric association suggest this delineation represents the vestiges of an ancient border between Mesolithic hunter-gatherer and Neolithic farmer populations, undetectable in other regions of Europe. This study provides further insight into the development of the current population structure and clarifies the resolution of uniparental marker variation in contemporary Finland, with implications for forensic applications such as ancestryinformative testing. Since unusual population structures are known to affect the applicability of forensic testing, a variety of markers were tested in the Finnish population in order to ensure validity. Along with the aforementioned population stratification, Finland’s unusual history has also left its mark on the population in the form of reduced diversity, visible especially in the Y-chromosome. Unlike elsewhere in Europe, neither the standard 9-locus Y-microsatellite set, nor more powerful commercial multiplex kits are enough for satisfactory resolution of male profiles in Finland. In order to improve the efficiency of Finnish Y-profiling, novel multiplex panels of highly polymorphic Y-microsatellite markers were developed and evaluated. The new 7and 24-locus Y-STR panels demonstrate improved suitability for practical forensic applications, with enhanced discrimination power and a reduction in regional subdivision compared to commercial sets. This study highlights the need for careful population-specific validation of commercial marker sets widely in use in forensics. Population-specific validation is especially necessary when adopting novel tools. In order to assess the applicability of a novel commercial panel of insertion-deletion markers in Finnish forensic profiling, the Investigator DIPplex kit was evaluated in the Finnish population. Earlier studies of the applicability of insertion/deletion polymorphisms as a tool of forensics had indicated that they were likely to be beneficial for casework analysis both in individual identification as well as the testing of familial relationships. The results of this study suggest that while these markers were well suited for individualization purposes, they were inefficient for paternity testing in the Finnish population. The genetic architecture of a population can also affect forensic disciplines outside the realm of individual identification, such as medico-legal investigations. Population bottlenecks can result in the enrichment of mutations, including those with clinical effects. The assessment of metabolic gene ABCB1 polymorphisms in Finns found increased frequency of these mutations in comparison to other populations. A further investigation performed on post-mortem samples revealed a positive correlation between mutation frequency and level of blood digoxin, suggesting that Finns may demonstrate an increased susceptibility to drug intoxication. These findings will aid forensic medicine by providing valuable additional evidence for molecular autopsies. A thorough understanding of underlying patterns of genetic variation and the history that created them is vital in recognizing the factors affecting practical forensic analysis today. In these studies, the deep genetic delineation between Eastern and Western regions of Finland was observed in a variety of forensic loci, and shown for the first time to extend also to mitochondrial markers, giving further evidence of its ancient history. The results of this thesis thus reveal new information about the history and demographics of the Finnish population while offering globally applicable improvements to forensic typing. The end result is more straightforward analysis and improved reliability for a spectrum of forensic applications ranging from individualization to cause of death determinations.