A New String Edit Distance and Applications

String edit distances have been used for decades in applications ranging from spelling correction and web search suggestions to DNA analysis. Most string edit distances are variations of the Levenshtein distance and consider only single-character edits. In forensic applications polymorphic genetic markers such as short tandem repeats (STRs) are used. At these repetitive motifs the DNA copying errors consist of more than just single base differences. More often the phenomenon of “stutter” is observed, where the number of repeated units differs (by whole units) from the template. To adapt the Levenshtein distance to be suitable for forensic applications where DNA sequence similarity is of interest, a generalized string edit distance is defined that accommodates the addition or deletion of whole motifs in addition to single-nucleotide edits. A dynamic programming implementation is developed for computing this distance between sequences. The novelty of this algorithm is in handling the complex interactions that arise between multiple- and single-character edits. Forensic examples illustrate the purpose and use of the Restricted Forensic Levenshtein (RFL) distance measure, but applications extend to sequence alignment and string similarity in other biological areas, as well as dynamic programming algorithms more broadly

An introductory overview of open-source and commercial software options for the analysis of forensic sequencing data

The top challenges of adopting new methods to forensic DNA analysis in routine laboratories are often the capital investment and the expertise required to implement and validate such methods locally. In the case of next-generation sequencing, in the last decade, several specifically forensic commercial options became available, offering reliable and validated solutions. Despite this, the readily available expertise to analyze, interpret and understand such data is still perceived to be lagging behind. This review gives an introductory overview for the forensic scientists who are at the beginning of their journey with implementing next-generation sequencing locally and because most in the field do not have a bioinformatics background may find it difficult to navigate the new terms and analysis options available. The currently available open-source and commercial software for forensic sequencing data analysis are summarized here to provide an accessible starting point for those fairly new to the forensic application of massively parallel sequencing

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; starlike 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

Massively Parallel Sequencing Of Forensic Markers: Sequence Variation And Forensic Application

DNA analyses have been used to aid forensic investigations since 1985 and to date, human identification relies on the typing of polymorphic autosomal short tandem repeats (STRs), supplemented by the use of paternal (Y-chromosomal STRs) and maternal (mitochondrial DNA; mtDNA) lineage markers. To accurately measure the significance of matching genotypes/haplotypes their frequencies in relevant populations must be estimated.Massively parallel sequencing (MPS) technologies became more cost-effective and therefore more accessible to forensic analysis in the last decade. Many markers and marker types can be simultaneously analysed to observe underlying sequence variants beyond simple length-variation. The distribution of sequence-level variants within and between populations also helps to illuminate population substructure.In this study, STRs and mtDNA were analysed using MPS first in a diverse global set of samples to establish a framework of variants beyond any single population, followed by the population analysis of a set of 362 samples from the People of the British Isles (PoBI) collection, chosen to represent the core population with minimal admixture in the last two generations. Available data from PoBI also allowed Y-SNP-defined haplogroups to be studied.Using MPS in these sample sets allowed the description of new STR variants, both within the sequence structure of repeat arrays and their flanking nucleotides. Analysis of the mtDNA control region following PCR with a multi-primer system revealed the importance of accounting for reference sequence bias in data analysis.The PoBI sample provided an overview of sequence-level variants of forensic markers across The British Isles, and serves as a reference for future MPS-based forensic applications. While mtDNA and autosomal markers show no appreciable population substructure, Y-chromosomal variation revealed clear East-West differentiation, probably reflecting a male-mediated Anglo-Saxon cultural and demographic shift around 500 CE, and correlating with current Celtic-Germanic linguistic divisions.</div

An Introductory Overview of Open-Source and Commercial Software Options for the Analysis of Forensic Sequencing Data

The top challenges of adopting new methods to forensic DNA analysis in routine laboratories are often the capital investment and the expertise required to implement and validate such methods locally. In the case of next-generation sequencing, in the last decade, several specifically forensic commercial options became available, offering reliable and validated solutions. Despite this, the readily available expertise to analyze, interpret and understand such data is still perceived to be lagging behind. This review gives an introductory overview for the forensic scientists who are at the beginning of their journey with implementing next-generation sequencing locally and because most in the field do not have a bioinformatics background may find it difficult to navigate the new terms and analysis options available. The currently available open-source and commercial software for forensic sequencing data analysis are summarized here to provide an accessible starting point for those fairly new to the forensic application of massively parallel sequencing

A New String Edit Distance and Applications

String edit distances have been used for decades in applications ranging from spelling correction and web search suggestions to DNA analysis. Most string edit distances are variations of the Levenshtein distance and consider only single-character edits. In forensic applications polymorphic genetic markers such as short tandem repeats (STRs) are used. At these repetitive motifs the DNA copying errors consist of more than just single base differences. More often the phenomenon of ``stutter'' is observed, where the number of repeated units differs (by whole units) from the template. To adapt the Levenshtein distance to be suitable for forensic applications where DNA sequence similarity is of interest, a generalized string edit distance is defined that accommodates the addition or deletion of whole motifs in addition to single-nucleotide edits. A dynamic programming implementation is developed for computing this distance between sequences. The novelty of this algorithm is in handling the complex interactions that arise between multiple- and single-character edits. Forensic examples illustrate the purpose and use of the Restricted Forensic Levenshtein (RFL) distance measure, but applications extend to sequence alignment and string similarity in other biological areas, as well as dynamic programming algorithms more broadly.Comment: 24 pages, 3 figures. Submitted to MDPI Algorithm

Mitigating the effects of reference sequence bias in single-multiplex massively parallel sequencing of the mitochondrial DNA control region.

Sequence analysis of the mitochondrial DNA (mtDNA) control region can provide forensically useful information, particularly in challenging samples where autosomal DNA profiling fails. Sub-division of the 1122-bp region into shorter PCR fragments improves data recovery, and such fragments can be analysed together via massively parallel sequencing (MPS). Here, we generate mtDNA data using the prototype PowerSeq™ Auto/Mito/Y System (Promega) MPS assay, in which a single PCR reaction amplifies ten overlapping amplicons of the control region, in a set of 101 highly diverse samples representing most major clades of the mtDNA phylogeny. The overlapping multiplex design leads to non-uniform coverage in the regions of overlap, where it is further increased by short amplicons generated alongside the intended products. Primer sequences in targeted amplification libraries are a potential source of reference sequence bias and thus should be removed, but the proprietary nature of the primers in commercial kits necessitates an alternative approach that minimises data loss: here, we introduce the bioinformatic selection of sequencing reads spanning putative primer sites (Overarching Read Enrichment Option, OREO). While OREO performs well in mitigating the effects of primer sequences at the ends of sequence reads, we still find evidence of the internalisation of primer-derived sequences by overlap extension, which may compromise the ability to call variants or to measure heteroplasmy in primer-binding regions. The commercially available PowerSeq™ CRM Nested System design prevents primer internalisation, as shown in a reanalysis of a subset of 57 samples that contain possible heteroplasmies. In combination with OREO, the CRM Nested kit mitigates reference sequence bias, allowing heteroplasmic variants to be estimated down to a 5% threshold. Provided appropriate steps are taken in data processing, single-reaction multiplex assays represent robust tools to analyse mtDNA control region variation. The OREO approach will allow users to bypass the effects of unknown primer sequences in any single-reaction tiled multiplex and eliminate primer-derived bias in overlapping amplicon sequencing studies, in both forensic and non-forensic settings

A phylogenetic framework facilitates Y-STR variant discovery and classification via massively parallel sequencing

Short-tandem repeats on the male-specific region of the Y chromosome (Y-STRs) are permanently linked as haplotypes, and therefore Y-STR sequence diversity can be considered within the robust framework of a phylogeny of haplogroups defined by single-nucleotide polymorphisms (SNPs). Here we use massively parallel sequencing (MPS) to analyse the 23 Y-STRs in Promega’s prototype PowerSeqÔ Auto/Mito/Y System kit (containing the markers of the PowerPlex® Y23 [PPY23] System) in a set of 100 diverse Y chromosomes whose phylogenetic relationships are known from previous megabase-scale resequencing. Including allele duplications and alleles resulting from likely somatic mutation, we characterised 2311 alleles, demonstrating 99.83% concordance with capillary electrophoresis (CE) data on the same sample set. The set contains 267 distinct sequence-based alleles (an increase of 58% compared to the 169 detectable by CE), including 60 novel Y-STR variants phased with their flanking sequences which have not been reported previously to our knowledge. Variation includes 46 distinct alleles containing non-reference variants of SNPs/indels in both repeat and flanking regions, and 145 distinct alleles containing repeat pattern variants (RPV). For DYS385a,b, DYS481 and DYS390 we observed repeat count variation in short flanking segments previously considered invariable, and suggest new MPS-based structural designations based on these. We considered the observed variation in the context of the Y phylogeny: several specific haplogroup associations were observed for SNPs and indels, reflecting the low mutation rates of such variant types; however, RPVs showed less phylogenetic coherence and more recurrence, reflecting their relatively high mutation rates. In conclusion, our study reveals considerable additional diversity at the Y-STRs of the PPY23 set via MPS analysis, demonstrates high concordance with CE data, facilitates nomenclature standardisation, and places Y-STR sequence variants in their phylogenetic context