Subdividing Y-chromosome haplogroup R1a1 reveals Norse Viking dispersal lineages in Britain.

The influence of Viking-Age migrants to the British Isles is obvious in archaeological and place-names evidence, but their demographic impact has been unclear. Autosomal genetic analyses support Norse Viking contributions to parts of Britain, but show no signal corresponding to the Danelaw, the region under Scandinavian administrative control from the ninth to eleventh centuries. Y-chromosome haplogroup R1a1 has been considered as a possible marker for Viking migrations because of its high frequency in peninsular Scandinavia (Norway and Sweden). Here we select ten Y-SNPs to discriminate informatively among hg R1a1 sub-haplogroups in Europe, analyse these in 619 hg R1a1 Y chromosomes including 163 from the British Isles, and also type 23 short-tandem repeats (Y-STRs) to assess internal diversity. We find three specifically Western-European sub-haplogroups, two of which predominate in Norway and Sweden, and are also found in Britain; star-like features in the STR networks of these lineages indicate histories of expansion. We ask whether geographical distributions of hg R1a1 overall, and of the two sub-lineages in particular, correlate with regions of Scandinavian influence within Britain. Neither shows any frequency difference between regions that have higher (≥10%) or lower autosomal contributions from Norway and Sweden, but both are significantly overrepresented in the region corresponding to the Danelaw. These differences between autosomal and Y-chromosomal histories suggest either male-specific contribution, or the influence of patrilocality. Comparison of modern DNA with recently available ancient DNA data supports the interpretation that two sub-lineages of hg R1a1 spread with the Vikings from peninsular Scandinavia.

DNA Commission of the International Society for Forensic Genetics (ISFG): Guidelines on the use of X-STRs in kinship analysis.

Forensic genetic laboratories perform an increasing amount of genetic analyses of the X chromosome, in particular to solve complex cases of kinship analysis. For some biological relationships X-chromosomal markers can be more informative than autosomal markers, and there are a large number of markers, methods and databases that have been described for forensic use. Due to their particular mode of inheritance, and their physical location on a single chromosome, some specific considerations are required when estimating the weight of evidence for X-chromosomal marker DNA data. The DNA Commission of the International Society for Forensic Genetics (ISFG) hereby presents guidelines and recommendations for the use of X-chromosomal markers in kinship analysis with a special focus on the biostatistical evaluation. Linkage and linkage disequilibrium (association of alleles) are of special importance for such evaluations and these concepts and the implications for likelihood calculations are described in more detail. Furthermore it is important to use appropriate computer software that accounts for linkage and linkage disequilibrium among loci, as well as for mutations. Even though some software exist, there is still a need for further improvement of dedicated software.

Evaluation of the impact of genetic linkage in forensic identity and relationship testing for expanded DNA marker sets.

Advances in massively parallel sequencing technology have enabled the combination of a much-expanded number of DNA markers (notably STRs and SNPs in one or combined multiplexes), with the aim of increasing the weight of evidence in forensic casework. However, when data from multiple loci on the same chromosome are used, genetic linkage can affect the final likelihood calculation. In order to study the effect of linkage for different sets of markers we developed the biostatistical tool ILIR, (Impact of Linkage on forensic markers for Identity and Relationship tests). The ILIR tool can be used to study the overall impact of genetic linkage for an arbitrary set of markers used in forensic testing. Application of ILIR can be useful during marker selection and design of new marker panels, as well as being highly relevant for existing marker sets as a way to properly evaluate the effects of linkage on a case-by-case basis. ILIR, implemented via the open source platform R, includes variation and genomic position reference data for over 40 STRs and 140 SNPs, combined with the ability to include additional forensic markers of interest. The use of the software is demonstrated with examples from several different established marker sets (such as the expanded CODIS core loci) including a review of the interpretation of linked genetic data.

A SNP panel for identity and kinship testing using massive parallel sequencing.

Within forensic genetics, there is still a need for supplementary DNA marker typing in order to increase the power to solve cases for both identity testing and complex kinship issues. One major disadvantage with current capillary electrophoresis (CE) methods is the limitation in DNA marker multiplex capability. By utilizing massive parallel sequencing (MPS) technology, this capability can, however, be increased. We have designed a customized GeneRead DNASeq SNP panel (Qiagen) of 140 previously published autosomal forensically relevant identity SNPs for analysis using MPS. One single amplification step was followed by library preparation using the GeneRead Library Prep workflow (Qiagen). The sequencing was performed on a MiSeq System (Illumina), and the bioinformatic analyses were done using the software Biomedical Genomics Workbench (CLC Bio, Qiagen). Forty-nine individuals from a Swedish population were genotyped in order to establish genotype frequencies and to evaluate the performance of the assay. The analyses showed to have a balanced coverage among the included loci, and the heterozygous balance showed to have less than 0.5 % outliers. Analyses of dilution series of the 2800M Control DNA gave reproducible results down to 0.2 ng DNA input. In addition, typing of FTA samples and bone samples was performed with promising results. Further studies and optimizations are, however, required for a more detailed evaluation of the performance of degraded and PCR-inhibited forensic samples. In summary, the assay offers a straightforward sample-to-genotype workflow and could be useful to gain information in forensic casework, for both identity testing and in order to solve complex kinship issues.

FamLinkX - implementation of a general model for likelihood computations for X-chromosomal marker data.

The use of genetic markers located on the X chromosome has seen a significant increase in the last years and their utility has been well studied. This paper describes the software FamLinkX, freely available at http://www.famlink.se, implementing a new algorithm for likelihood computations accounting for linkage, linkage disequilibrium and mutations. It is obvious that such software is sought for among forensic users as more and more X-chromosomal markers become available. We provide some simulated examples demonstrating the utility of the implementation as well as its application in forensic casework. Though algebraic derivations are generally unfeasible, the paper outlines some theoretical considerations and provides a discussion on the validation of the software. The focus of this paper is to compare the software to existing methods in a forensic setting, perform a validation study as well as to provide an idea of the discriminatory power for X-chromosomal markers.

Familias 3 - Extensions and new functionality.

In relationship testing the aim is to determine the most probable pedigree structure given genetic marker data for a set of persons. Disaster Victim Identification (DVI) based on DNA data from presumed relatives of the missing persons can be considered to be a collection of relationship problems. Forensic calculations in investigative mode address questions like "How many markers and reference persons are needed?" Such questions can be answered by simulations. Mutations, deviations from Hardy-Weinberg Equilibrium (or more generally, accounting for population substructure) and silent alleles cannot be ignored when evaluating forensic evidence in case work. With the advent of new markers, so called microvariants have become more common. Previous mutation models are no longer appropriate and a new model is proposed. This paper describes methods designed to deal with DVI problems and a new simulation model to study distribution of likelihoods. There are softwares available, addressing similar problems. However, for some problems including DVI, we are not aware of freely available validated software. The Familias software has long been widely used by forensic laboratories worldwide to compute likelihoods in relationship scenarios, though previous versions have lacked desired functionality, such as the above mentioned. The extensions as well as some other novel features have been implemented in the new version, freely available at www.familias.no. The implementation and validation are briefly mentioned leaving complete details to Supplementary sections.

Choosing supplementary markers in forensic casework.

The vast majority of human familial identifications based on DNA end up with a well founded conclusion, normally using a standard set of genetic short tandem repeat (STR) loci. There are, however, a proportion of cases that show ambiguous results. For such occasions a number of different supplementary markers could be typed in order to gain further information. There are numerous markers available for such supplementary DNA typing, including STRs, deletion and insertion polymorphisms (DIPs), and single nucleotide polymorphisms (SNPs). The purpose of this work was to describe a precise method for decision making, aiming to aid the comparison of different sets of markers for different case scenarios in order to find the most efficient set for routine casework. Comparisons are based on a particular function relating the expected additional value of information from new data to the amount of information already obtained from initial data. The function can be computed approximately by approximating likelihood-based error rates using simulation. In this paper we focused on paternity investigations, more specifically the use of supplementary markers in cases where a smaller number of genetic inconsistencies make the matter inconclusive. We applied the method to a comparison of three different kits: Investigator HDplex (STRs), Investigator DIPplex (DIPs), and the SNPforID-plex (SNPs) to study their efficiencies in gaining information in different case scenarios involving various alternative relationships between the tested man and the tested child. We show that the Investigator HDplex was the most efficient set of supplementary markers for the standard paternity case. However, for paternity cases with a close relative being the alternative father, the Investigator HDplex and the SNPforID-plex showed similar patterns in their ability to deliver a well-founded conclusion. The Investigator DIPplex was the least efficient set.

Population genetics of 29 autosomal STRs and 17 Y-chromosomal STRs in a population sample from Afghanistan.

In this study, allele frequencies for 29 autosomal short tandem repeats (STRs) and haplotype frequencies for 17 Y-chromosomal STRs of an Afghan population have been generated. Samples from 348 men and women originating from Afghanistan were analysed for the autosomal STRs, and the combined match probability was estimated to be 7.5 × 10(-37). One hundred and sixty-nine men were analysed for the Y-chromosomal STRs, which resulted in 132 different haplotypes and a haplotype diversity of 0.995.

A universal method for species identification of mammals utilizing next generation sequencing for the analysis of DNA mixtures.

Species identification can be interesting in a wide range of areas, for example, in forensic applications, food monitoring and in archeology. The vast majority of existing DNA typing methods developed for species determination, mainly focuses on a single species source. There are, however, many instances where all species from mixed sources need to be determined, even when the species in minority constitutes less than 1 % of the sample. The introduction of next generation sequencing opens new possibilities for such challenging samples. In this study we present a universal deep sequencing method using 454 GS Junior sequencing of a target on the mitochondrial gene 16S rRNA. The method was designed through phylogenetic analyses of DNA reference sequences from more than 300 mammal species. Experiments were performed on artificial species-species mixture samples in order to verify the method's robustness and its ability to detect all species within a mixture. The method was also tested on samples from authentic forensic casework. The results showed to be promising, discriminating over 99.9 % of mammal species and the ability to detect multiple donors within a mixture and also to detect minor components as low as 1 % of a mixed sample.

Effect of linkage between vWA and D12S391 in kinship analysis.

Ideally for use in forensic analyses, genetic markers on the same chromosome should be more than 50 Mb in physical distance to ensure full recombination and thus independent inheritance. The forensic community has given attention to two STR markers, D12S391 and vWA, that are 6.3 megabases (Mb) apart on chromosome 12. Recent studies have shown no significant linkage disequilibrium between vWA and D12S391 in U.S. and worldwide populations, although genetic linkage has been identified. It is important to evaluate the impact of linkage effects on kinship analysis. In this study, we aimed to determine a more precise measurement of the recombination frequency between vWA and D12S391 based on a larger number of informative meiosis than has been studied previously. We estimated the recombination frequency (θ) to 0.089 (95% CI 0.044-0.158). Using pedigrees simulated under specific kinship scenarios where recombination was expected to affect the likelihood ratio (LR), we evaluated the impact on LR values of including or ignoring linkage between vWA and D12S391. For all pedigree scenarios considered, on average, LR values ignoring linkage were slightly underestimated than when linkage was considered. However, in the incest scenario considered, LR values could be overestimated up to 25-30 times when linkage was ignored. We demonstrate that the effect of ignoring linkage in the likelihood ratio calculation can be considerable. These results suggest that linkage should be considered during kinship analysis when vWA and D12S391 are tested for pedigrees where a recombination could impact the LR value.

FamLink--a user friendly software for linkage calculations in family genetics.

The present number of STR loci adopted in relationship testing is chiefly limited to unlinked markers, in most cases residing on different chromosomes. In order to solve more complex cases of relatedness, e.g. deficient paternities and disputed sibships, the number of core loci can be extended. The inclusion of multiple loci on the same chromosome will, however, increase the risk of possible linkage between markers. We present a new software, FamLink, freely available from http://www.FamLink.se, that can perform statistical calculations based on pedigree structures and account for linkage between pairs of markers. In addition, FamLink can simulate genotype data in order to study the effect of accounting for linkage or not. We demonstrate the importance of taking linkage properly into account using examples and real cases.

Using X-chromosomal markers in relationship testing: calculation of likelihood ratios taking both linkage and linkage disequilibrium into account.

X-chromosomal markers in forensic genetics have become more widely used during recent years, particularly for relationship testing. Linkage and linkage disequilibrium (LD) must typically be accounted for when using close X-chromosomal markers. Thus, when producing the weight-of-evidence, given by a DNA-analysis with markers that are linked, the normally used product rule is invalid. Here we present an implementation of an efficient model for calculating likelihood ratios (LRs) with markers on the X-chromosome which are linked and in LD. Furthermore, the model was applied on several cases based on data from the eight X-chromosomal loci included in the Mentype(®) Argus X-8 (Biotype). Using a simulation approach we showed that the use of X-chromosome data can offer valuable information for choosing between the alternatives in each of the cases we studied, and that the LR can be high in several cases. We demonstrated that when linkage and LD were disregarded, as opposed to taken into account, the difference in calculated LRs could be considerable. When these differences were large, the estimated haplotype frequencies often had a strong impact and we present a method to estimate haplotype frequencies. Our conclusion is that linkage and LD should be accounted for when using the tested set of markers, and the used model is an efficient way of doing so.

Homogeneity in mitochondrial DNA control region sequences in Swedish subpopulations.

In order to promote mitochondrial DNA (mtDNA) testing in Sweden we have typed 296 Swedish males, which will serve as a Swedish mtDNA frequency database. The tested males were taken from seven geographically different regions representing the contemporary Swedish population. The complete mtDNA control region was typed and the Swedish population was shown to have high haplotype diversity with a random match probability of 0.5%. Almost 47% of the tested samples belonged to haplogroup H and further haplogroup comparison with worldwide populations clustered the Swedish mtDNA data together with other European populations. AMOVA analysis of the seven Swedish subregions displayed no significant maternal substructure in Sweden (F (ST) = 0.002). Our conclusion from this study is that the typed Swedish individuals serve as good representatives for a Swedish forensic mtDNA database. Some caution should, however, be taken for individuals from the northernmost part of Sweden (provinces of Norrbotten and Lapland) due to specific demographic conditions. Furthermore, our analysis of a small sample set of a Swedish Saami population confirmed earlier findings that the Swedish Saami population is an outlier among European populations.

Genetic variation of 15 autosomal STR loci in a Somali population.

Allele frequencies for 15 autosomal STR loci included in the AmpFlSTR Identifiler kit (CSF1PO, D13S317, D16S539, D18S51, D19S433, D21S11, D2S1338, D3S1358, D5S818, D7S820, D8S1179, FGA, TH01, TPOX, VWA) were obtained from the analysis of 404 individuals with Somali origin. The overall match probability for the 15 studied loci was 1 in 1.18 x 10(17) and the combined power of exclusion was 0.999997676. Deviation from Hardy-Weinberg equilibrium was observed for locus D2S1338 after correction for multiple testing. When comparing allele frequencies with five other African populations (Karamoja (Uganda), Mozambique, Tanzania and two other Somali population sample sets), only the Somali populations did not show significant differences for any of the tested loci.

Analysis of linkage and linkage disequilibrium for eight X-STR markers.

X-chromosomal short tandem repeats (X-STR) have proven to be informative and useful in complex relationship testing. The main feature of X-STR markers, compared to autosomal forensic markers, is that all loci are located on the same chromosome. Thus, linkage and linkage disequilibrium may occur. The aim of this work was to study population genetic parameters of eight X-STR markers, located in four linkage groups. We present haplotype frequencies, based on 718 Swedish males, for the four linkage groups included in the Argus X-8 kit. Forensic efficiency parameters have been calculated as well as the allelic association between the tested markers for detection of linkage disequilibrium. To study the occurrences of recombination between the loci, both Swedish and Somali families were typed. A mathematical model for the estimation of recombination frequencies is presented and applied on the family samples. Our study showed that the tested markers all have highly informative forensic values and that there is a significant degree of linkage disequilibrium between the STR markers within the four linkage groups. Furthermore, based on the tested families, we also demonstrated that two of the linkage groups are partially linked. A consequence of these findings is that both linkage and linkage disequilibrium should be accounted for when producing likelihood ratios in relationship testing with X-STR markers.