A multi-dimensional evaluation of the 'NIST 1032' sample set across four forensic Y-STR multiplexes

Bed bugs, Cimex lectularius: Undercover agents in forensic investigations

Insects have long played a role in forensic investigations and can be used to estimate minimum time since death, corpse translocation, and link an individual to a crime scene. Bed bugs (Cimex lectularius) are wingless ectoparasitic insects of potential forensic utility, given that all mobile life stages feed on vertebrate blood. Successful profiling of autosomal short tandem repeats (STRs) from human DNA isolated from bed bugs has been previously reported. This proof-of-concept study looked to expand this work and determine any possible limitations of using bed bugs for both rapid stain identification (RSID™) for human blood and Y-STR profiling. To achieve this, bed bugs were fed either human male only or human pooled (female:male) blood for 30 min and subsequently collected at 12-h intervals up to 108 h post-blood meal (PBM). RSID™ blood testing was successful from the bed bug carcass remaining after DNA isolation, regardless of blood meal type and time of collection PBM. Complete Y-STR profiles were generated from bed bugs <60 h PBM. As the time PBM increased, DNA quantity decreased, while the degradation index increased. Collection of bed bugs at a crime scene could provide a valuable source of human blood for Y STR profiling and be used to link an individual to a crime scene or for potential male suspect exclusion. Future studies should look to replicate the results of this proof-of-concept study with larger numbers of bed bugs, more diverse blood donors, and additional STR profiling kits.

Uncertainty in the number of contributor estimation methods applied to a Y-STR profile

Maximum allele count (MAC) and total allele count (TAC) methods are widely used for estimating the number of contributors (NoC) of autosomal short tandem repeat (STR) profile in many forensic laboratories. In this study, we applied NoC estimation methods to mixed Y-STR profiles and evaluated its uncertainty and performance. For the MAC method, as recent Y-STR typing kits involve single- and multi-copy loci, we defined "MAC-single" for use across only single-copy loci and "MAC-multi" for use across only multi-copy loci. We generated a dataset containing 120,000 Y-STR profiles for a one to six-person mixture in silico based on previously reported haplotype frequencies of 27 Y-STR loci in Yfiler Plus for the U.S. population (reported by NIST) and the Henan Han population. The dataset was randomly split into a training set and a test set. The training set was used to construct a TAC distribution (TAC curve), whereas the test set was used to calculate the performance metrics (accuracy, precision, recall, and F1-score). In addition, the effect of the upper limit of NoC considered for estimation on overall accuracy was evaluated. The overall accuracies of MAC-single, MAC-multi, and TAC methods when the upper limit of NoC was set to six-person were 0.7920, 0.4329, and 0.7877 for the U.S. population and 0.8207, 0.4609, and 0.8385 for the Henan Han population. Our results suggest that the MAC-single and TAC methods can estimate the NoC for mixed Y-STR profiles with high levels of accuracy.

Evaluating the efficacy of three Y-STRs commercial kits in degraded skeletal remains

Y chromosome short tandem repeats (Y-STRs) typing is a useful tool in scenarios such as mass graves analysis or disaster victim identification and has become a routine analysis in many laboratories. Not many comparisons have been performed with the currently available commercial kits, much less with degraded skeletal remains. This research aims to evaluate the performance of three commercial Y-STR kits: Yfiler™ Plus, PowerPlex® Y23, and Investigator® Argus Y-28 in 63 degraded skeletal remains from mass graves. PowerPlex® Y23 yields more reportable markers and twice the RFU on average, while Yfiler™ Plus and Investigator® Argus Y-28 exhibited a similar behaviour. Additionally, Argus Y-28, which has not been tested with this kind of samples in literature before, showed a good performance. Finally, a predictive model was attempted to be developed from quantification and autosomal STR data. However, no acceptable model could be obtained. Nevertheless, good Y-STR typing results may be expected if at least 50 pg DNA input is used or 13 autosomal markers were previously obtained.

Considerations on the application of a mutation model for Y-STR interpretation

If Y-STR profiling is to be more effective in criminal casework, the methods used to evaluate evidential weight require improvement. Many forensic scientists assign an evidential weight by estimating the number of times a Y-STR profile obtained from a questioned sample has been observed in YHRD datasets. More sophisticated models have been suggested but not yet implemented into routine casework, e.g. Andersen & Balding [1]. Mutation is inherent to STR meiosis (or inheritance) and is encountered in practice. We evaluated a mutation model that can be incorporated into a method for assigning evidential weight to Y-STR profiles, an essential part of bringing any method into practice. Since an important part of implementation to casework is communication, the article is written in an accessible format for practitioners as well as statisticians. The mutation component within the MUTEA model by Willems et al. [2] incorporates the potential for multistep mutations and a tendency for alleles to revert towards a central length, reflecting observed mutation data, e.g. [3]. We have estimated the parameters in this model and in a simplified symmetric version of this model, using sequence data from father/son pairs [4] and deep-rooted pedigrees [5]. Both datasets contain multistep mutations, which may have an effect on models based on simulations [1]. We introduce Beta-Binomial and Beta-Geometric conjugate analyses for estimating rate and step parameters for the mutation models presented here, which require only summations and multiplications. We proved mathematically that the parameters can be estimated independently. We show the importance of reporting the variability of the parameters and not only a point estimate. The parameters can be easily incorporated into statistical models, and updated sequentially as more data becomes available. We recommend fuller publication of data to enable the development and evaluation of a wider range of mutation models.

Concordance study on Y-STRs typing between SeqStudio™ genetic analyzer for HID and MiSeq™ FGx forensic genomics system

BACKGROUND

Massively Parallel Sequencing (MPS) allowed an increased number of information to be retrieved from short tandem repeat (STR) analysis, expanding them not only to the size, as already performed in Capillary Electrophoresis (CE), but also to the sequence. MPS requires constant development and validation of the analytical parameters to ensure that the genotyping results of STRs correspond to those obtained by CE. Given the increased frequency of usage of Y-STRs as supplementary markers to the autosomal STRs analysis, it is urgent to validate the concordance of the typing results between CE and MPS analyses.

METHODS AND RESULTS

DNA extracted from 125 saliva samples of unrelated males was genotyped using Yfiler™ Plus PCR Amplification Kit and ForenSeq™ DNA Signature Prep Kit, which were analyzed by SeqStudio™ Genetic Analyzer for HID and MiSeq™ FGx Forensic Genomics System, respectively. For each shared Y-STR, allele designation, number of length- and sequence-based alleles per locus, stutter percentage, and the intra-locus balance of multicopy Y-STRs were screened.

CONCLUSIONS

Although the number of forensic genetics laboratories that are applying the MPS technique in routine analysis is small and does not allow a global assessment of MPS limitations, this comparative study highlights the ability of MPS to produce reliable profiles despite the generation of large amounts of raw data.

US Population Data for 94 Identity-Informative SNP Loci

The US National Institute of Standards and Technology (NIST) analyzed a set of 1036 samples representing four major US population groups (African American, Asian American, Caucasian, and Hispanic) with 94 single nucleotide polymorphisms (SNPs) used for individual identification (iiSNPs). The compact size of iiSNP amplicons compared to short tandem repeat (STR) markers increases the likelihood of successful amplification with degraded DNA samples. Allele frequencies and relevant forensic statistics were calculated for each population group as well as the aggregate population sample. Examination of sequence data in the regions flanking the targeted SNPs identified additional variants, which can be combined with the target SNPs to form microhaplotypes (multiple phased SNPs within a short-read sequence). Comparison of iiSNP performance with and without flanking SNP variation identified four amplicons containing microhaplotypes with observed heterozygosity increases of greater than 15% over the targeted SNP alone. For this set of 1036 samples, comparison of average match probabilities from iiSNPs with the 20 CODIS core STR markers yielded an estimate of 1.7 × 10^-38 for iiSNPs (assuming independence between all 94 SNPs), which was four orders of magnitude lower (more discriminating) than STRs where internal sequence variation was considered, and 10 orders of magnitude lower than STRs using established capillary electrophoresis length-based genotypes.

High-resolution genotyping of 58 STRs in 635 Northern Han Chinese with MiSeq FGx ® Forensic Genomics System

Sequence polymorphisms were characterized at 27 autosomal STRs (A-STRs), 7 X chromosomal STRs (X-STRs), and 24 Y chromosomal STRs (Y-STRs) in 635 Northern Han Chinese with the ForenSeq DNA Signature Prep Kit on the MiSeq FGx Forensic Genomics System. Since repeat region (RR) and flanking region (FR) variation can be detected by massively parallel sequencing (MPS), the increase in the number of unique alleles and the average of gene diversity was 78.18% and 3.51% between sequence and length, respectively. A total of 74 novel RR variants were identified at 33 STRs compared with STRSeq and previous studies, and 13 FR variants (rs1770275883, rs2053373277, rs2082557941, rs1925525766, rs1926380862, rs1569322793, rs2051848492, rs2051848696, rs2016239814, rs2053269960, rs2044518192, rs2044536444, and rs2089968964) were first submitted to dbSNP. Also, 99.94% of alleles were concordant between the ForenSeq DNA Signature Prep Kit and commercial CE kits. Discordance resulted from the low performance at D22S1045 and occasionally at DYS392, flanking region deletions at D7S820 and DXS10074, and the strict alignment algorithm at DXS7132. Null alleles at DYS505 and DYS448 and multialleles at DYS387S1a/b, DYS385a/b, DYS448, DYS505, DXS7132, and HPRTB were validated with other MPS and CE kits. Thus, a high-resolution sequence-based (SB) and length-based (LB) allele frequencies dataset from Northern Han Chinese has been established already. As expected, forensic parameters increased significantly on combined power of discrimination (PD) and combined power of exclusion (PE) at A-STRs, mildly on combined PD and combined mean exclusion chance (MEC) at X-STRs, and barely on discrimination capacity (DC) at Y-STRs. Additionally, MiSeq FGx quality metrics and MPS performance were evaluated in this study, which presented the high-quality of the dataset at 20 consecutive runs, such as ≥ 60% bases with a quality score of 20 or higher (%≥ Q20), > 60% of effective reads, > 2000 × of depth of coverage (DoC), ≥ 60% of allele coverage ratio (ACR) or heterozygote balance, ≥ 70% of inter-locus balance, and ≤ 0.4 of the absolute value of observed minus expected heterozygosity (|H_exp - H_obs|). In conclusion, MiSeq FGx can help us generate a high-resolution and high-quality dataset for human identification and population genetic studies.

Genetic polymorphisms and phylogenetic characteristics of Tibeto-Burman-speaking Lahu population from southwest China based on 41 Y-STR loci

BACKGROUND

Male sex-linked Y-chromosome short tandem repeats (Y-STRs) have been widely used in forensic cases and population genetics research. At present, the forensic-related Y-STR data in the Chinese Lahu population are still poorly understood.

AIM

To enrich the available Y-STR data of this Chinese minority population and investigate its phylogenetic relationships with other reported populations.

SUBJECTS AND METHODS

The genetic polymorphisms of 41 Y-STR loci were analysed in 299 unrelated healthy Lahu male individuals from Southwest China. Phylogenetic analyses were performed by multidimensional scaling analysis and neighbor-joining phylogenetic tree construction.

RESULTS

A total of 379 alleles were observed at the 41 Y-STR loci. The allele frequencies ranged from 0.0033 to 0.9666. The genetic diversity values ranged from 0.0653 to 0.9072. A total of 254 different haplotypes of the 41 Y-STR loci were observed in 299 individuals. The values of haplotype diversity, haplotype match probability, and discrimination capacity were 0.9987, 0.0047, and 0.8495, respectively. The phylogenetic analysis indicated that the Tibeto-Burman-speaking Lahu population showed a close genetic relationship with the Yunnan Yi population.

CONCLUSIONS

The haplotype data of the present study can enrich the forensic databases of this Chinese minority population and will be useful for population genetics and forensic DNA application.

Development and validation of a new multiplex for upgrading Y-STRs population databases from 12 to 23 markers and its forensic casework application

Y chromosomal short tandem repeats (Y-STRs) are used in forensic investigations as a useful complementary tool to autosomal markers. The ongoing development of new kits with an increasing number of markers makes it necessary to update populations typed in the Y-STR Haplotype Reference Database to reach at least 23 Y-STRs. A novel Y-STR multiplex panel was developed to offer a cost-efficient alternative to update Y-STR haplotypes from 12 to 23 loci. This panel includes the eleven markers, DYS448, DYS456, DYS458, DYS635, Y-GATA H4, DYS576, DYS481, DYS549, DYS533, DYS570 and DYS643, as well as DYS385a/b for traceability purpose. Developmental validation of this panel was conducted following the recommendations of the Scientific Working Group on DNA Analysis Methods (SWGDAM), showing high sensitivity, tolerance to common inhibitors as well as high species specificity. It was efficient for degraded DNA samples and for detection of male mixtures. When applying it for extending the current data of the Ibiza population, both the discrimination capacity and the haplotype diversity increased from 0.5952 to 0.9048 and from 0.9808 to 0.9977, respectively. Together, the study demonstrates the suitability of this panel in forensic casework.

On the Forensic Use of Y-Chromosome Polymorphisms

Nowadays, the use of Y-chromosome polymorphisms forms an essential part of many forensic DNA investigations. However, this was not always the case. Only since 1992 have we seen that some forensic scientists started to have an interest in this chromosome. In this review, I will sketch a brief history focusing on the forensic use of Y-chromosome polymorphisms. Before describing the various applications of short-tandem repeats (STRs) and single nucleotide polymorphisms (SNPs) on the Y-chromosome, I will discuss a few often ignored aspects influencing proper use and interpretation of Y-chromosome information: (i) genotyping Y-SNPs and Y-STRs, (ii) Y-STR haplotypes shared identical by state (IBS) or identical by descent (IBD), and (iii) Y-haplotype database frequencies.