Toward male individualization with rapidly mutating y-chromosomal short tandem repeats

Harmonizing the forensic nomenclature for STR loci D6S474 and DYS612

The autosomal STR D6S474 and the Y-chromosomal STR DYS612 have been reported in multiple ways in the forensic literature, with differences in both the bracketed repeat structures and counting of numerical length-based capillary electrophoresis (CE) alleles. These issues often come to light when STR loci are introduced in commercial assays and results compared with historical publications of allele frequency data, or multiple assays are characterized with reference materials. We review the forensic literature and other relevant information, and provide suggestions for the future treatment of each STR.

Microsatellites' mutation modeling through the analysis of the Y-chromosomal transmission: Results of a GHEP-ISFG collaborative study

The Spanish and Portuguese Speaking Working Group of the International Society for Forensic Genetics (GHEP-ISFG) organized a collaborative study on mutations of Y-chromosomal short tandem repeats (Y-STRs). New data from 2225 father-son duos and data from 44 previously published reports, corresponding to 25,729 duos, were collected and analyzed. Marker-specific mutation rates were estimated for 33 Y-STRs. Although highly dependent on the analyzed marker, mutations compatible with the gain or loss of a single repeat were 23.2 times more likely than those involving a greater number of repeats. Longer alleles (relatively to the modal one) showed to be nearly twice more mutable than the shorter ones. Within the subset of longer alleles, the loss of repeats showed to be nearly twice more likely than the gain. Conversely, shorter alleles showed a symmetrical trend, with repeat gains being twofold more frequent than reductions. A positive correlation between the paternal age and the mutation rate was observed, strengthening previous findings. The results of a machine learning approach, via logistic regression analyses, allowed the establishment of algebraic formulas for estimating the probability of mutation depending on paternal age and allele length for DYS389I, DYS393 and DYS627. Algebraic formulas could also be established considering only the allele length as predictor for DYS19, DYS389I, DYS389II-I, DYS390, DYS391, DYS393, DYS437, DYS439, DYS449, DYS456, DYS458, DYS460, DYS481, DYS518, DYS533, DYS576, DYS626 and DYS627 loci. For the remaining Y-STRs, a lack of statistical significance was observed, probably as a consequence of the small effective size of the subsets available, a common difficulty in the modeling of rare events as is the case of mutations. The amount of data used in the different analyses varied widely, depending on how the data were reported in the publications analyzed. This shows a regrettable waste of produced data, due to inadequate communication of the results, supporting an urgent need of publication guidelines for mutation studies.

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.

Improving the strategy to identify historical military remains: a literature review and Y-STR meta-analysis

The identification of historical military remains by Unrecovered War Casualties-Army (UWC-A) currently relies on Y-chromosome Short Tandem Repeat (Y-STR) testing when maternal relatives are not available, or when a mitochondrial DNA match does not provide sufficient certainty of identification. However, common Y-STR profiles (using Yfiler™) between sets of remains or families often prevent identification. To resolve these cases, an investigation of additional Y-DNA markers is needed for their potential inclusion into the DNA identification strategy. The number of genetic transmissions between missing soldiers and their living relatives needs to be considered to avoid false exclusions between paternal relatives. Analysis of 236 World War I/II (WWI/II) era pairs of relatives identified up to seven genetic transmissions between WWII soldiers and their living relatives, and nine for WWI. Previous Y-STR meta-analyses were published approximately 10 years ago when rapidly mutating markers were relatively new. This paper reports a contemporary literature review and meta-analysis of 35 studies (which includes 23 studies not previously used in meta-analysis) and 23 commonly used Y-STR's mutation rates to inform the inclusion of additional loci to UWC-A's DNA identification strategy. Meta-analysis found mutation data for a given Y-STR locus could be pooled between studies and that the mutation rates were significantly different between some loci (at P < 0.05). Based on this meta-analysis, we have identified two additional markers from PowerPlex® Y23 for potential inclusion in UWC-A's identification strategy. Further avenues for potential experimental exploration are discussed.

Key points

From 236 UWC-A pairs of relatives, we observed up to nine genetic transmissions between WWI soldiers and their living relatives, and seven for WWII.MedCalc® software for meta-analysis utilizing the Freeman-Tukey transformation was run, which analysed 35 published studies and 23 commonly used loci. Previous Y-STR mutation rate meta-analyses are now 10 years old; this paper includes 23 studies that were not included in previous meta-analyses.Through meta-analysis, we identify two markers from PowerPlex® Y23 for potential inclusion in UWC-A's historical remains identification strategy (alongside Yfiler™). We discuss potential next steps for experimental exploration of additional Y-DNA markers.

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.

Unraveling the paternal genetic structure and forensic traits of the Hui population in Liaoning Province, China using Y-chromosome analysis

The Hui people are the second-largest ethnic minority in China, and they are distributed throughout the country. A previous study explored the paternal genetic structure of the Hui population in nine different regions of China, but it overlooked the Liaoning province. In this study, we examined the paternal genetic makeup and forensic traits of the Hui population in Liaoning province by analyzing 157 Y-chromosome single nucleotide polymorphisms (Y-SNPs) and 26 short tandem repeats (Y-STRs). We successfully genotyped 282 unrelated male individuals from the Hui population of Liaoning province using the SNaPshot® single base extension assay and Goldeneye™ Y26 system kit (PEOPLESPOT R&D, Beijing, China). The results revealed high haplotypic diversity (0.9998) and identified 46 terminal haplogroups for the Hui population. Additional analyses, such as heat maps, principal component analysis (PCA), genetic distance (FST), Multidimensional scaling (MDS) analysis, and median-joining network (MJ) analysis, showed that the Hui population could be classified into three groups: Northwest Hui populations (NWH), including Liaoning, Xinjiang, Qinghai, Gansu, Ningxia, Shaanxi, and Henan; Hui populations from Sichuan and Shandong (SSH); and Yunnan Hui populations (YNH). Pairwise genetic distance (Rst) comparisons with other Chinese populations revealed that the Hui population displayed genetic affinity with the Han population. The comprehensive understanding of the Hui population in Liaoning province, explored by Y-SNPs and Y-STRs, can be utilized to interpret their genetic structure and enhance the accuracy of forensic databases.

The sequence of the repetitive motif influences the frequency of multistep mutations in Short Tandem Repeats

Microsatellites, or Short Tandem Repeats (STRs), are subject to frequent length mutations that involve the loss or gain of an integer number of repeats. This work aimed to investigate the correlation between STRs' specific repetitive motif composition and mutational dynamics, specifically the occurrence of single- or multistep mutations. Allelic transmission data, comprising 323,818 allele transfers and 1,297 mutations, were gathered for 35 Y-chromosomal STRs with simple structure. Six structure groups were established: ATT, CTT, TCTA/GATA, GAAA/CTTT, CTTTT, and AGAGAT, according to the repetitive motif present in the DNA leading strand of the markers. Results show that the occurrence of multistep mutations varies significantly among groups of markers defined by the repetitive motif. The group of markers with the highest frequency of multistep mutations was the one with repetitive motif CTTTT (25% of the detected mutations) and the lowest frequency corresponding to the group with repetitive motifs TCTA/GATA (0.93%). Statistically significant differences (α = 0.05) were found between groups with repetitive motifs with different lengths, as is the case of TCTA/GATA and ATT (p = 0.0168), CTT (p < 0.0001) and CTTTT (p < 0.0001), as well as between GAAA/CTTT and CTTTT (p = 0.0102). The same occurred between the two tetrameric groups GAAA/CTTT and TCTA/GATA (p < 0.0001) - the first showing 5.7 times more multistep mutations than the second. When considering the number of repeats of the mutated paternal alleles, statistically significant differences were found for alleles with 10 or 12 repeats, between GATA and ATT structure groups. These results, which demonstrate the heterogeneity of mutational dynamics across repeat motifs, have implications in the fields of population genetics, epidemiology, or phylogeography, and whenever STR mutation models are used in evolutionary studies in general.

Internal validation of an improved system for forensic application: a 41-plex Y-STR panel

Y-chromosome short tandem repeats (Y-STRs) have a unique role in forensic investigation. However, low-medium mutating Y-STRs cannot meet the requirements for male lineage differentiation in inbred populations, whereas rapidly mutating (RM) high-resolution Y-STRs might cause unexpected exclusion of paternal lineages. Thus, combining Y-STRs with low and high mutation rates helps to distinguish male individuals and lineages in family screening and analysis of genetic relationships. In this study, a novel 6-dye, 41-plex Y-STR panel was developed and validated, which included 17 loci from the Yfiler kit, nine RM Y-STR loci, 15 low-medium mutating Y-STR loci, and three Y-InDels. Developmental validation was performed for this panel, including size precision testing, stutter analysis, species specificity analysis, male specificity testing, sensitivity testing, concordance evaluation, polymerase chain reaction inhibitors analysis, and DNA mixture examination. The results demonstrated that the novel 41-plex Y-STR panel, developed in-house, was time efficient, accurate, and reliable. It showed good adaptability to directly amplify a variety of case-type samples. Furthermore, adding multiple Y-STR loci significantly improved the system's ability to distinguish related males, making it highly informative for forensic applications. In addition, the data obtained were compatible with the widely used Y-STR kits, facilitating the search and construction of population databases. Moreover, the addition of Y-Indels with short amplicons improves the analyses of degraded samples.

Key Points

A novel multiplex comprising 41 Y-STR and 3 Y-InDel was developed for forensic application.The multiplex included rapidly mutating Y-STRs and low-medium mutating Y-STRs, which is compatible with many commonly used Y-STR kits.The multiplex is a powerful tool for distinguishing related males, familial searching, and constructing DNA databases.

Biogeographic origin and genetic characteristics of the peopling of Jeju Island based on lineage markers

BACKGROUND

Jeju Island is the largest island of South Korea, located southwest far from the mainland of Korea, and has a unique history and its own cultures that are distinguished from those of the other regions of the Korean mainland. However, the Jeju population has not been deeply investigated to date to understand their genetic structure, which may reflect their historical and geographical background.

OBJECTIVE

To identify the genetic characteristics and biogeographic origin of people of Jeju Island based on the statistical analysis of genetic data using lineage markers.

METHODS

17 Y-STRs data for 615 unrelated males and mitochondrial DNA haplogroup data for 799 unrelated individuals residing on Jeju Island were generated, and analyzed to investigate genetic diversity and genetic characteristics using statistical methods including pairwise Fst or Rst, Analysis of molecular variance (AMOVA) and Multidimensional scaling (MDS).

RESULTS

For male individuals of Jeju Island, unique genetic characteristics were observed in the analysis of Y-STRs, including low haplotype diversity, strong association with surnames, genetic difference from other regions of Korea, and common genetic variation of the Y-STR loci known to be predominant in Northern populations, such as Mongolians. Statistical analysis of the mitochondrial DNA haplogroups also revealed similar results that showed low haplogroup diversity and high frequency of haplogroup Y prevalent mostly in ethnic populations around the Sea of Okhotsk in Northeastern Asia. All these results suggest that Jeju Island is genetically distinct from other regions of Korea, possibly being a subpopulation in Korea, and related closely to Northern Asian populations.

CONCLUSION

The findings in the genetic approach could support understanding of the historical background of Jeju Island that is consistent with evidence from other multidisciplinary studies.

[Polymorphism and Mutation Rate of 20 Rapidly Mutating Y-Chromosomal Short Tandem Repeats in Chinese Han Population of Sichuan Province]

Objective

To explore the applicability of 20 rapidly mutating Y-chromosomal short tandem repeats (RM Y-STRs) in Chinese Han population of Sichuan province.

Methods

Two RM Y-STR multiple amplification systems (RM1, including DYF404S1, DYF399S1, DYS547, DYS526a/b, DYS626, DYF403S1a/b, and DYS612, and RM2, including DYS1003, DYS1007, DYR88, DYS712, DYS711, DYS724, and DYF1002, with 14 RM Y-STR loci in total) and Y41SE-V1.2 (including 6 RM Y-STR loci of DYS627, DYS576, DYF387S1, DYS518, DYS570, and DYS449, 30 ordinary Y-chromosomal short tandem repeats [Y-STR] loci, and 1 Indel locus) were used for the amplification and typing of 200 unrelated males and 260 father-son pairs. The polymorphisms and mutation rates of 20 RM Y-STRs and 30 ordinary Y-STRs in Chinese Han population of Sichuan province were investigated and compared.

Results

In the 200 unrelated males, the gene diversity (GD) of 20 RM Y-STR loci ranged from 0.7910 to 0.9975, and there were 200 haplotypes. Haplotype diversity (HD) was 1 and the discriminative capacity (DC) was 1. A total of 198 haplotypes were found in Y41se-v1.2 (the 30 Y-STRs), with 4 cases sharing two haplotypes, the haplotype diversity being 0.9999, and the discriminative capacity being 0.99. A total of 68 mutations were found at the 20 RM Y-STRs loci in the 260 father-son pairs, and there was slightly more increase than decrease of allele repeats (1.19∶1), with the mutation rate ranging from <3.85×10 -3 (95% C I: 0.00-1.41×10 -2) to 2.69×10 -2 (95% CI: 1.09×10 -2-5.47×10 -2), and the average mutation rate being 1.19×10 -2 (95% CI: 9.20×10 -3-1.51×10 -2). The 20 RM Y-STRs and the Y41SE-V1.2 (the 30 Y-STRs) could be used to distinguish 22.3% and 13.8% father-son pairs, respectively.

Conclusion

The 20 RM Y-STRs have high gene and haplotype diversity and paternal lineage differentiation rate in Chinese Han population of Sichuan province, showing great potential for application in Chinese Han population of Sichuan province.

Large-scale pedigree analysis highlights rapidly mutating Y-chromosomal short tandem repeats for differentiating patrilineal relatives and predicting their degrees of consanguinity

Rapidly mutating Y-chromosomal short tandem repeats (RM Y-STRs) were suggested for differentiating patrilineally related men as relevant in forensic genetics, anthropological genetics, and genetic genealogy. Empirical data are available for closely related males, while differentiation rates for more distant relatives are scarce. Available RM Y-STR mutation rate estimates are typically based on father-son pair data, while pedigree-based studies for efficient analysis requiring less samples are rare. Here, we present a large-scale pedigree analysis in 9379 pairs of men separated by 1-34 meioses on 30 Y-STRs with increased mutation rates including all known RM Y-STRs (RMplex). For comparison, part of the samples were genotyped at 25 standard Y-STRs mostly with moderate mutation rates (Yfiler Plus). For 43 of the 49 Y-STRs analyzed, pedigree-based mutation rates were similar to previous father-son based estimates, while for six markers significant differences were observed. Male relative differentiation rates from the 30 RMplex Y-STRs were 43%, 84%, 96%, 99%, and 100% for relatives separated by one, four, six, nine, and twelve meioses, respectively, which largely exceeded rates obtained by 25 standard Y-STRs. Machine learning based models for predicting the degree of patrilineal consanguinity yielded accurate and reasonably precise predictions when using RM Y-STRs. Fully matching haplotypes resulted in a 95% confidence interval of 1-6 meioses with RMplex compared to 1-25 with Yfiler Plus. Our comprehensive pedigree study demonstrates the value of RM Y-STRs for differentiating male relatives of various types, in many cases achieving individual identification, thereby overcoming the largest limitation of forensic Y-chromosome analysis.

Comparison between MACSprep™ forensic sperm microbead kit and Erase Sperm Isolation kit for the enrichment of sperm fractions recovered from sexual assault samples

Sexual assault samples often contain mixtures of cells coming from at least two donors. Ideally, one would need to separate the cells into two cellular fractions: one consisting of the alleged aggressor's spermatozoa (the sperm fraction) and the other containing the victim's epithelial cells (the non-sperm fraction). This separation increases the probability of obtaining the alleged offender's autosomal DNA profile. However, spermatozoa are often collected along with an excess of biological material originating from the victim, and with unfavorable male:female biological material ratios, the absence of separation could result in the PCR amplification of the victim's DNA profile only. Several approaches are available to enrich/purify the spermatozoa present on sexual assault samples. In this paper, we compare a new method, the MACSprep™ Forensic Sperm MicroBead Kit (MACSprep, based on microbeads conjugated with antibodies bound to spermatozoa and their retention within a magnetic column) with the Erase Sperm Isolation Kit (Erase, a standard differential lysis separation procedure combined with a specific removal of free DNA) routinely used in our lab. The performance of both kits was tested using sets of vaginal and buccal swabs loaded with different dilutions of sperm, or azoospermic semen, representing a total of 120 independent samples. For the samples containing undiluted sperm, an average recovery of 58% was observed for the MACSprep's sperm fractions and 43% for Erase's. Significantly better recovery of azoospermic semen was observed in MACSprep's non-sperm fractions (~ 85%) compared to Erase (~ 28%). Erase performed significantly better than MACSprep in terms of recovery for diluted sperm samples (1:10 to 1:800 sperm dilutions) in the presence of vaginal cells, while the purities of the achieved sperm fractions were in favor of MACSprep for the highest sperm dilutions tested. Similar trends were observed with buccal swabs loaded with 1:200 sperm dilutions. Increased sperm dilutions on vaginal swabs resulted in higher variability in the male material recovered, whatever the separation method used. Both methods were easy to perform and resulted in male DNA extracts ready to use in less than 2 h. Both kits showed their specificities in terms of recovery efficiency and purity of the sperm fractions. Ideally, additional experiments should be performed in different laboratories, using workflow and chemistries different than ours, to better define the peculiarities observed with MACSprep for high dilutions. Improving the recovery of MACSprep for diluted samples, in addition to its better purity observed in the experiments performed, could make it a method of choice for laboratory workflow, despite MACSprep's current price per sample being about twice the price of Erase's.

Design and development of novel single multiplex system incorporating 26 rapidly mutating Y-STRs; 26 RM Yplex

This article details the development of a single multiplex system amplifying 26 rapidly mutating Y-STR markers. A sequenced allelic ladder, constructed for calling alleles of all loci, is introduced. The multiplex system shows the ability to address the limitations of Y-STRs commercial kits in differentiating closely related males. The multiplex performed well in the prevalidation tests and showed great potential to be used in forensic casework.

RMplex reveals population differences in RM Y-STR mutation rates and provides improved father-son differentiation in Japanese

Rapidly mutating Y chromosomal short tandem repeat markers (RM Y-STRs) -characterized by at least one mutation per 100 generations- are suitable for differentiating both related and unrelated males. The recently introduced multiplex method RMplex allows for the efficient analysis of 30 Y-STRs with increased mutation rates, including all 26 currently known RM Y-STRs. While currently available RM Y-STR mutation rates were established mostly from European individuals, here we applied RMplex to DNA samples of 178 genetically confirmed father-son pairs from East Asia. For several Y-STRs, we found significantly higher mutation rates in Japanese compared to previous estimates. The consequent father-son differentiation rate based on RMplex was significantly higher (52%) in Japanese than previously reported for Europeans (42%), and much higher than with Yfiler Plus in both sample sets (14% and 13%, respectively). Further analysis suggests that the higher mutation and relative differentiation rates in Japanese can in part be explained by on average longer Y-STR alleles relative to Europeans. Moreover, we show that the most striking difference, which was found in DYS712, could be linked to a Y-SNP haplogroup (O1b2-P49) that is common in Japanese and rare in other populations. We encourage the forensic Y-STR community to generate more RMplex data from more population samples of sufficiently large sample size in combination with Y-SNP data to further investigate population effects on mutation and relative differentiation rates. Until more RMplex data from more populations become available, caution shall be placed when applying RM Y-STR mutation rate estimates established in one population, such as Europeans, to forensic casework involving male suspects of paternal origin from other populations, such as non-Europeans.

Mutation Rate Analysis of RM Y-STRs in Deep-Rooted Multi-Generational Punjabi Pedigrees from Pakistan

Y chromosome short tandem repeat polymorphisms (Y-STRs) are important in many areas of human genetics. Y chromosomal STRs, being normally utilized in the field of forensics, exhibit low haplotype diversity in consanguineous populations and fail to discriminate among male relatives from the same pedigree. Rapidly mutating Y-STRs (RM Y-STRs) have received much attention in the past decade. These 13 RM Y-STRs have high mutation rates (>10−2) and have considerably higher haplotype diversity and discrimination capacity than conventionally used Y-STRs, showing remarkable power when it comes to differentiation in paternal lineages in endogamous populations. Previously, we analyzed two to four generations of 99 pedigrees with 1568 pairs of men covering one to six meioses from all over Pakistan and 216 male relatives from 18 deep-rooted endogamous Sindhi pedigrees covering one to seven meioses. Here, we present 861 pairs of men from 62 endogamous pedigrees covering one to six meioses from the Punjabi population of Punjab, Pakistan. Mutations were frequently observed at DYF399 and DYF403, while no mutation was observed at DYS526a/b. The rate of differentiation ranged from 29.70% (first meiosis) to 80.95% (fifth meiosis), while overall (first to sixth meiosis) differentiation was 59.46%. Combining previously published data with newly generated data, the overall differentiation rate was 38.79% based on 5176 pairs of men related by 1−20 meioses, while Yfiler differentiation was 9.24% based on 3864 pairs. Using father−son pair data from the present and previous studies, we also provide updated RM Y-STR mutation rates.

Empirical Evidence on Enhanced Mutation Rates of 19 RM-YSTRs for Differentiating Paternal Lineages

Rapidly mutating Y-chromosomal short tandem repeats (RM Y STRs) with mutation rates ≥ 10⁻² per locus per generation are valuable for differentiating amongst male paternal relatives where standard Y STRs with mutation rates of ≤10⁻³ per locus per generation may not. Although the 13 RM Y STRs commonly found in commercial assays provide higher levels of paternal lineage differentiation than conventional Y STRs, there are many male paternal relatives that still cannot be differentiated. This can be improved by increasing the number of Y STRs or choosing those with high mutation rates. We present a RM Y STR multiplex comprising 19 loci with high mutation rates and its developmental validation (repeatability, sensitivity and male specificity). The multiplex was found to be robust, reproducible, specific and sensitive enough to generate DNA profiles from samples with inhibitors. It was also able to detect all contributor alleles of mixtures in ratios up to 9:1. We provide preliminary evidence for the ability of the multiplex to discriminate between male paternal relatives by analyzing large numbers of male relative pairs (536) separated by one to seven meioses. A total of 96 mutations were observed in 162 meioses of father–son pairs, and other closely related male pairs were able to be differentiated after 1, 2, 3, 4, 5, 6 and 7 meiosis in 44%, 69%, 68%, 85%, 0%, 100% and 100% of cases, respectively. The multiplex offers a noticeable enhancement in the ability to differentiate paternally related males compared with the 13 RM Y STR set. We envision the future application of our 19 RM Yplex in criminal cases for the exclusion of male relatives possessing matching standard Y STR profiles and in familial searching with unknown suspects. It represents a step towards the complete individualization of closely related males.

Developmental Validation of a Rapidly Mutating Y-STR Panel Labeled by Six Fluoresceins for Forensic Research

The male-specific region of the human Y chromosome is a useful genetic marker for genealogical searching, male inheritance testing, and male DNA mixture deconvolution in forensic studies. However, the Y chromosomal short tandem repeats (Y-STRs) are difficult to distinguish among related males due to their low/medium mutation rate. In contrast, rapidly mutating (RM) Y-STRs exhibit unusually high mutation rates and possess great potential for differentiating male lineages. In this study, we developed a novel Y-STRs multiplex amplification assay of 32 RM Y-STRs by fragment analysis using six dye-labeled technologies (FAM, HEX, TAMRA, ROX, VIG, and SIZ). The development and the validation of the kit were carried out in accordance with the Scientific Working Group guidelines on DNA Analysis Methods. Identical allelic profiles of the 32 RM Y-STRs using a DNA 9948 sample as the positive control could be observed at different concentrations of PCR reagents. Further, the RM Y-STRs did not show cross-reactions with other common animal species, and the developed assay could tolerate interferences from common PCR inhibitors and mixed DNA samples. More importantly, the kit showed relatively high sensitivity and could detect trace DNA samples. Genetic distributions of 32 RM Y-STRs in the Guizhou Han population revealed that these RM Y-STRs showed relatively high genetic diversities. In conclusion, the RM Y-STR assay developed here showed good species specificity, high sensitivity, tolerance to inhibitors, and sample compatibility, which can be viewed as a highly efficient tool with high discrimination capacity for forensic male differentiation.

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

This manuscript reports Y-chromosomal short tandem repeat (Y-STR) haplotypes for 1032 male U.S. population samples across 30 Y-STR loci characterized by three capillary electrophoresis (CE) length-based kits (PowerPlex Y23 System, Yfiler Plus PCR Amplification Kit, and Investigator Argus Y-28 QS Kit) and one sequence-based kit (ForenSeq DNA Signature Prep Kit): DYF387S1, DYS19, DYS385 a/b, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS448, DYS449, DYS456, DYS458, DYS460, DYS481, DYS505, DYS518, DYS522, DYS533, DYS549, DYS570, DYS576, DYS612, DYS627, DYS635, DYS643, and Y-GATA-H4. The length-based Y-STR haplotypes include six loci that are not reported in the sequence-based kit (DYS393, DYS449, DYS456, DYS458, DYS518, and DYS627), whereas three loci included in the sequence-based kit are not present in length-based kits (DYS505, DYS522, and DYS612). For the latter, a custom multiplex was used to generate CE length-based data, allowing 1032 samples to be evaluated for concordance across the 30 Y-STR loci included in these four commercial Y-STR typing kits. Discordances between typing methods were analyzed further to assess underlying causes such as primer binding site mutations and flanking region insertions/deletions. Allele-level frequency and statistical information is provided for sequenced loci, excluding the multi-copy loci DYF387S1 and DYS385 a/b, for which locus-specific haplotype-level frequencies are provided instead. The resulting data reveals the degree of information gained through sequencing: 88% of sequenced Y-STR loci contain additional sequence-based alleles compared to length-based data, with the DYS389II locus containing the most additional alleles (51) observed by sequencing. Despite these allelic increases, only minimal improvement was observed in haplotype resolution by sequence, with all four commercial kits providing a similar ability to differentiate length-based haplotypes in this sample set. Finally, a subset of 369 male samples were compared to their corresponding additionally sequenced father samples, revealing the sequence basis for the 50 length-based changes observed, and no additional sequence-based mutations. GenBank accession numbers are reported for each unique sequence, and associated records are available in the STRSeq Y-Chromosomal STR Loci National Center for Biotechnology Information (NCBI) BioProject, accession PRJNA380347. Haplotype data is updated in the Y-STR Haplotype Reference Database (YHRD) for the 'NIST 1032' data set to now achieve the level of maximal haplotype of YHRD. All supplementary files including revisions to previously published Y-STR data are available in the NIST Public Data Repository: U.S. population data for human identification markers, DOI 10.18434/t4/1500024.

Sequence Variations of 31 Υ-Chromosomal Short Tandem Repeats Analyzed by Massively Parallel Sequencing in Three U.S. Population Groups and Korean Population

BACKGROUND

Rapidly mutating (RM) Y-chromosomal short tandem repeats (Y-STRs) have been demonstrated to increase the possibility of distinguishing between male relatives due to a higher mutation rate than conventional Y-STRs. Massively parallel sequencing (MPS) can be useful for forensic DNA typing as it allows the detection of sequence variants of many forensic markers. Here, we present sequence variations of 31 Y-STRs including nine RM Y-STRs (DYF387S1, DYF399S1, DYF404S1, DYS449, DYS518, DYS570, DYS576, DYS612, and DYS627), their frequencies, distribution, and the gain in the number of alleles using MPS.

METHODS

We constructed a multiplex MPS assay capable of simultaneously amplifying 32 Y-chromosomal markers, producing amplicons ranging from 85-274 bp. Barcoded libraries from 220 unrelated males from four populations-African Americans, Caucasians, Hispanics, and Koreans-were generated via two-step polymerase chain reaction and sequenced on a MiSeq system. Genotype concordance between the capillary electrophoresis (CE) and MPS method and sequence variation of Y-STRs were investigated.

RESULTS

In total, 195 alleles were increased by MPS compared to CE-based alleles (261 to 456). The DYS518 marker showed the largest increase due to repeat region variation (a 3.69-fold increase). The highest increase in the number of alleles due to single nucleotide polymorphisms in the flanking region was found in DYF399S1. RM Y-STRs had more diverse sequences than conventional Y-STRs. Furthermore, null alleles were observed in DYS576 due to primer-binding site mutation, and allele drop-outs in DYS449 resulted from low marker coverage of less than the threshold.

CONCLUSION

The results suggest that the expanded and discriminative MPS assay could provide more genetic information for Y-STRs, especially for RM Y-STRs, and could advance male individualization. Compiling sequence-based Y-STR data for worldwide populations would facilitate the application of MPS in the field of forensic genetics and could be applicable in solving male-related forensic cases.

The Validation of a Single Multiplex Typing System With 45 Y-STR Markers for Familial Searching and Database Construction

The Y-chromosomal short tandem repeat (Y-STR) is an effective forensic tool in familial searches and patrilineal relationship evaluation. However, currently available Y-STR panels often lack sufficient discriminatory power to resolve genetic relationships between distant relatives or within patrilocal populations. This study aims to establish a novel Y-STR amplification system for forensic casework analysis and database construction, which contains 44 slowly and moderately mutating and one rapidly mutating Y-STR. The validation of the assay was conducted following the recommendations of SWGDAM developmental validation guidelines. Different types of casework samples were tested and reliable profiles were obtained. Furthermore, we genotyped and analyzed 141 unrelated Han Chinese male samples. The results showed that this Y45 kit could improve the performance of identifying male individuals, higher haplotype diversity, and discrimination capacity when compared to the previous widely used Yfiler Plus kit. In general, the validation study demonstrated that the newly developed Y45 kit possesses high sensitivity, inhibitor tolerance, male specificity in a mixture, species specificity, and precision and is capable of forensic casework analysis and database construction.

Improving the regional Y-STR haplotype resolution utilizing haplogroup-determining Y-SNPs and the application of machine learning in Y-SNP haplogroup prediction in a forensic Y-STR database: A pilot study on male Chinese Yunnan Zhaoyang Han population

Improving the resolution of the current widely used Y-chromosomal short tandem repeat (Y-STR) dataset is of great importance for forensic investigators, and the current approach is limited, except for the addition of more Y-STR loci. In this research, a regional Y-DNA database was investigated to improve the Y-STR haplotype resolution utilizing a Y-SNP Pedigree Tagging System that includes 24 Y-chromosomal single nucleotide polymorphism (Y-SNP) loci. This pilot study was conducted in the Chinese Yunnan Zhaoyang Han population, and 3473 unrelated male individuals were enrolled. Based on data on the male haplogroups under different panels, the matched or near-matching (NM) Y-STR haplotype pairs from different haplogroups indicated the critical roles of haplogroups in improving the regional Y-STR haplotype resolution. A classic median-joining network analysis was performed using Y-STR or Y-STR/Y-SNP data to reconstruct population substructures, which revealed the ability of Y-SNPs to correct misclassifications from Y-STRs. Additionally, population substructures were reconstructed using multiple unsupervised or supervised dimensionality reduction methods, which indicated the potential of Y-STR haplotypes in predicting Y-SNP haplogroups. Haplogroup prediction models were built based on nine publicly accessible machine-learning (ML) approaches. The results showed that the best prediction accuracy score could reach 99.71% for major haplogroups and 98.54% for detailed haplogroups. Potential influences on prediction accuracy were assessed by adjusting the Y-STR locus numbers, selecting Y-STR loci with various mutabilities, and performing data processing. ML-based predictors generally presented a better prediction accuracy than two available predictors (Nevgen and EA-YPredictor). Three tree models were developed based on the Yfiler Plus panel with unprocessed input data, which showed their strong generalization ability in classifying various Chinese Han subgroups (validation dataset). In conclusion, this study revealed the significance and application prospects of Y-SNP haplogroups in improving regional Y-STR databases. Y-SNP haplogroups can be used to discriminate NM Y-STR haplotype pairs, and it is important for forensic Y-STR databases to develop haplogroup prediction tools to improve the accuracy of biogeographic ancestry inferences.

The Y chromosome and its use in forensic DNA analysis

Originally relatively ignored in forensic investigations because its genetic analysis lacks inference of individual identification, the value of Y chromosome analysis has been proven in cases of sexual assault, particularly where the amount of material left by a male assailant is limited in comparison with female DNA. All routine analysis of autosomal DNA, however, targets a gene (AMELY) on the Y chromosome in order to identify the sex of the DNA source and this is discussed in the context of the genetic structure of this male-specific chromosome. Short-tandem repeat markers on the chromosome are tested in dedicated multiplexes that have developed over time and these are described alongside international guidance as to their use in a forensic setting. As a marker of lineage, the Y chromosome provides additional tools to assist in the inference of ancestry, both geographical and familial and the value of Y chromosome testing is illustrated through descriptions of cases of criminal and historical interest. A decision to analyse the Y chromosome has to be considered in the context, not only of the circumstances of the case, but also with regard to the ethical questions it might raise, and these are discussed in relation to the cases that have been described in more detail in the accompanying online supplementary material.

RMplex: An efficient method for analyzing 30 Y-STRs with high mutation rates

Y-chromosomal short tandem repeats (Y-STRs) with high mutation rates are recognized as valuable genetic markers for differentiating paternally related men, who typically cannot be separated with standard Y-STRs, and were shown to provide paternal lineage differentiation on a higher resolution level than standard Y-STRs. Both features make Y-STRs with high mutation rates relevant in criminal casework, particularly in sexual assault cases involving highly unbalanced male-female DNA mixtures that often fail autosomal forensic STR profiling for the male donor. Previously, the number of known Y-STRs with mutation rates higher than 10^-2 per locus per generation termed rapidly mutating Y-STRs (RM Y-STRs) was limited to 13, which has recently been overcome by the discovery and characterization of 12 additional RM Y-STRs. Here, we present the development and validation of RMplex, an efficient genotyping system for analyzing 30 Y-STRs with high mutation rates, including all currently known RM Y-STRs, using multiplex PCR with capillary electrophoresis (CE) or massively parallel sequencing (MPS), overall targeting a total of 44 male-specific loci. If previously unavailable, repeat number assignations were provided based on newly generated MPS data. Validation tests based on the CE method demonstrated that the results were both repeatable and reproducible, full profiles were achieved with minimal input DNA of 250 pg for RMplex 1 and 100 pg for RMplex 2, and in the presence of inhibitors, or with a surplus of female DNA, the assays performed reasonably well. Application of RMplex to differentiate between paternally related men was exemplified in 32 males belonging to five different paternal pedigrees. Given further successful forensic validation testing, we envision the future application of RMplex in criminal cases where it is suspected, or cannot be excluded, that the crime scene trace originated from a male relatives of the suspect who is highlighted with standard Y-STR matching. Other applications of RMplex are in criminal cases without known suspects to differentiate between male relatives highlighted in familial searching based on standard Y-STR matching.

CSYseq: The first Y-chromosome sequencing tool typing a large number of Y-SNPs and Y-STRs to unravel worldwide human population genetics

Male-specific Y-chromosome (chrY) polymorphisms are interesting components of the DNA for population genetics. While single nucleotide polymorphisms (Y-SNPs) indicate distant evolutionary ancestry, short tandem repeats (Y-STRs) are able to identify close familial kinships. Detailed chrY analysis provides thus both biogeographical background information as paternal lineage identification. The rapid advancement of high-throughput massive parallel sequencing (MPS) technology in the past decade has revolutionized genetic research. Using MPS, single-base information of both Y-SNPs as Y-STRs can be analyzed in a single assay typing multiple samples at once. In this study, we present the first extensive chrY-specific targeted resequencing panel, the ‘CSYseq’, which simultaneously identifies slow mutating Y-SNPs as evolution markers and rapid mutating Y-STRs as patrilineage markers. The panel was validated by paired-end sequencing of 130 males, distributed over 65 deep-rooted pedigrees covering 1,279 generations. The CSYseq successfully targets 15,611 Y-SNPs including 9,014 phylogenetic informative Y-SNPs to identify 1,443 human evolutionary Y-subhaplogroup lineages worldwide. In addition, the CSYseq properly targets 202 Y-STRs, including 81 slow, 68 moderate, 27 fast and 26 rapid mutating Y-STRs to individualize close paternal relatives. The targeted chrY markers cover a high average number of reads (Y-SNP = 717, Y-STR = 150), easy interpretation, powerful discrimination capacity and chrY specificity. The CSYseq is interesting for research on different time scales: to identify evolutionary ancestry, to find distant family and to discriminate closely related males. Therefore, this panel serves as a unique tool valuable for a wide range of genetic-genealogical applications in interdisciplinary research within evolutionary, population, molecular, medical and forensic genetics.

Around 95% of the male-specific Y-chromosome (chrY) is non-recombining and therefore inherited in a conserved manner from father to son. It can therefore serve as a powerful marker for interdisciplinary genetic-genealogical research as it provides a strong link between genetic information and a family tree or pedigree. While Y-chromosomal short tandem repeats (Y-STRs) discriminate close paternal kinships, single nucleotide polymorphisms (Y-SNPs) enables the identification of far evolutionary ancestry. Unfortunately, an extensive chrY-specific sequencing panel combining a large number of familial Y-STRs and evolutionary Y-SNPs was not yet available. Therefore, chrY is rarely included in research projects and not often linked to a genealogical, history-demographical or life science database. In this way, the importance of chrY still remains not yet fully understood. Massive parallel sequencing (MPS) allows the simultaneous analysis at sequence level of Y-SNPs and Y-STRs with variable mutation rates in a large number of males. However, up until today, no commercial kit is exploiting the full potential that MPS offers on chrY. Therefore, we developed the ‘CSYseq’, which is the first extensive chrY-specific sequencing panel. The CSYseq simultaneously identifies 9,014 slow mutating Y-SNPs to identify evolutionary ancestry, and 202 rapid mutating Y-STRs to investigate paternal relationships. We validated and optimized the panel through the analysis of 130 males distributed over 65 families. This novel MPS panel is useful for biogeographical identity and ancestry analysis, together with Y-chromosome profiling for the identification of patrilineages and discrimination of closely related males. As the CSYseq includes a very diverse set of markers that can be easily interpreted, it is interesting for different interdisciplinary applications within evolutionary, population, molecular, medical and forensic genetics.

YMrCA: Improving Y-chromosomal ancestor time estimation for DNA kinship research

The Y-chromosome is a valuable kinship indicator in family history and forensic research. To reconstruct genealogies, the time to the most recent common ancestor (tMRCA) between paternal relatives can be estimated through Y-STR analysis. Existing models are the stepwise mutation model (SMM, only one-step Y-STR changes) and the infinite allele model (IAM, new allele per Y-STR change). In this study, these mutation models and all existing tMRCA calculators were validated through a genetic-genealogy database containing 1,120 biologically related genealogical pairs confirmed by 46 Y-STRs with known tMRCA (18,109 generations). Consistent under- and overestimation and broad confidence intervals were observed, leading to dubious tMRCA estimates. This is because they do not include individual mutation rates or multi-step changes and ignore hidden multiple, back, or parallel modifications. To improve tMRCA estimation, we developed a user-friendly calculator, the "YMrCA", including all previously mentioned mutation characteristics. After extensive validation, we observed that the YMrCA calculator demonstrated a promising performance. The YMrCA yields a significantly higher tMRCA success rate (96%; +20%) and a lower tMRCA error (7; -3) compared to the mutation models and all online tMRCA calculators. Therefore, YMrCA offers the next step towards more objective tMRCA estimation for DNA kinship research.

A novel multiplex of 12 multicopy Y-STRs for forensic application

Y chromosomal short tandem repeats (Y-STRs) have been applied overwhelmingly in forensic areas for solving paternity identification and sexual assault cases. Yet the widely used Y-STR kits contain mostly single-copy markers, which may restrict the discrimination power. Here, a novel Y-STR multiplex was developed and validated in order to complement the currently available Y-STR kits, especially on differentiating male relatives. The assay includes twelve multicopy Y-STR loci (DYF371, DYF383S1, DYS385, DYF387S1, DYS389I/II, DYF399S1, DYF404S1, DYF409S1, DYF411S1, DYS464, DYS526, DYS527; four of them are rapidly mutating ones), 1 single-copy Y-STR (DYS391), and Amelogenin, and was optimized to amplify at annealing temperature of 59°C and 28 cycles. Validation studies show that full profiles are obtained with 0.125 ng of male DNA. The system is capable of overcoming high concentrations of inhibitors such as hematin, EDTA, and humic acid. Besides, the results demonstrate good sizing precision and the ability to detect male-specific profiles in male/female DNA mixtures at a ratio of 1:800. Excellent species specificity was also observed in microorganisms and non-primates, while detectable peaks were found in some primates. Based on published genetic data, gene diversity values were above 0.7 for most of the loci in our multiplex, inferring a high capacity in discriminating unrelated and related male individuals. The kit is of great potential for forensic application.

The Y-STR landscape of coastal southeastern Han: Forensic characteristics, haplotype analyses, mutation rates, and population genetics

The Y-STR landscape of Coastal Southeastern Han (CSEH) living in Chinese southeast areas (including Guangdong, Fujian, and Zhejiang provinces) is still unclear. We investigated 62 Y-STR markers in a reasonably large number of 1021 unrelated males and 1027 DNA-confirmed father-son pairs to broaden the genetic backgrounds of CSEH. In total, 85 null alleles, 121 off-ladder alleles, and 95 copy number variants were observed, and 1012 distinct haplotypes were determined with the overall HD and DC values of 0.999974 and 0.9912. We observed 369 mutations in 76 099 meiotic transfers, and the average estimated Y-STR mutation rate was 4.85 × 10^-3 (95% CI, 4.4 × 10^-3 -5.4 × 10^-3 ). The Spearman correlation analyses indicated that GD values (R² = 0.6548) and average allele sizes (R² = 0.5989) have positive correlations with Y-STR mutation rates. Our RM Y-STR set including 8 candidate RM Y-STRs, of which DYS534, DYS630, and DYS713 are new candidates in CSEH, distinguished 18.52% of father-son pairs. This study also clarified the population structures of CSEH which isolated in population-mixed South China relatively. The strategy, SM Y-STRs for familial searching and RM Y-STRs for individual identification regionally, could be applicable based on enough knowledge of the Y-STR mutability of different populations.

Next generation sequencing of Y-STRs in father-son pairs and comparison with traditional capillary electrophoresis

To evaluate the promising advantages of massively parallel sequencing (MPS) in our casework, we analysed a total of 33 Y-chromosomal short tandem repeats (Y-STRs) with traditional capillary electrophoresis (CE) and 25 Y-STRs using the newer MPS technology. We studied the outcome of both technologies in 64 father-son pairs using stock and custom-designed kits. Current MPS technology confirmed the 13 mutational events observed with CE and improved our understanding of the complex nature of STR mutations. By detecting isometric sequence variants between unrelated males, we show that sequencing Y-STRs using MPS can boost discrimination power.

Haplotype diversity and phylogenetic relationship analysis of Chinese Yulin Han population using 59 Y-STR loci of two novel Y-STR typing systems

To investigate the genetic polymorphisms of 59 Y-chromosomal short tandem repeat (Y-STR) loci in the Yulin Han population, 229 unrelated healthy male individuals were analyzed using AGCU Y37 kit and AGCU Y-SUPP Plus kit. A total of 227 different haplotypes were obtained at the 59 Y-STR loci. Among them, 225 haplotypes were unique and 2 haplotypes occurred twice. The overall haplotypic diversity and discrimination capacity were 0.9999 and 0.9913, respectively. The phylogenetic relationships between the studied Yulin Han population and 17 previously reported reference populations were evaluated via multidimensional scaling and Neighbor-Joining analyses based on the haplotypic frequencies of 'YHRD Maximal Loci'. Phylogenetic analysis revealed that Yulin Han population was closely related to Chinese Han and Hunan Yao populations. These results demonstrated that the 59 Y-STR loci were useful for forensic applications and population genetic studies.

Genetic structure and forensic characterization of 36 Y-chromosomal STR loci in Tibeto-Burman-speaking Yi population

BACKGROUND

Male-specifically inherited Y-STRs have been widely used in population genetics and forensic investigations.

METHODS

We genotyped and analyzed Y chromosome haplotypes of 408 unrelated Tibeto-Burman-speaking Yi male individuals from Guizhou using Goldeneye® Y-PLUS kit. Population comparisons between the Guizhou Yi and 67 reference groups were performed via the AMOVA, MDS, and phylogenetic relationship reconstruction.

RESULTS

A total of 389 alleles and 396 haplotypes could be detected, and the allelic frequencies ranged from 0.0025 to 0.9875. The haplotype diversity, random match probability, and discrimination capacity values were 0.9999, 0.0026, and 0.9900, respectively. The gene diversity (GD) of 36 Y-STR loci in the studied group ranged from 0.0248 (DYS645) to 0.9601 (DYS385a/b). Our newly genotyped Yi samples show a close affinity with other Tibeto-Burman speaking groups in China and Southeast Asia.

CONCLUSIONS

The population stratification was almost consistent with the geographic distribution and language-family, both among Chinese and worldwide ethnic groups. Our data may provide useful information for paternal lineage in the forensic application and population genetics, as well as evidence for archaeological and historical research.

STRNaming: Generating simple, informative names for sequenced STR alleles in a standardised and automated manner

The introduction of Massively Parallel Sequencing in the forensic domain has exposed the need for comprehensive nomenclature of sequenced Short Tandem Repeat (STR) alleles. In general, three strategies are at hand: 1) the full sequence mapped to the human genome reference sequence, which ensures exact data exchange; 2) shortened, human-readable formats for forensic reporting and data presentation and 3) very short codes that enable compact figures and tables but do not convey any sequence information. Here, we describe an algorithm of the second type: STRNaming, which generates human-readable names for sequenced STR alleles. STRNaming is guided by a reference sequence at each locus and then functions independently to automatically assign a unique, sequence-descriptive name that also includes the capillary electrophoresis allele number. STRNaming settings were established based on preferences that were surveyed internationally in the forensic community. These settings ensure that a small change in the sequence corresponds to a small change in the allele name, which is helpful for recognising for instance stutter products. Sequence variants outside of the repeat units are indicated as simple variant calls. Since the STR name is sequence-descriptive, the sequence can be traced back from the allele name. Because STRNaming is fully guided by an assignable reference sequence, no central coordination or configuration is required and the method will work for any STR locus, be it autosomal, Y-, X-chromosomal in current or future use. The algorithm is publicly available online and offline.

Developmental validation of the Yfiler Platinum PCR Amplification Kit for forensic genetic caseworks and databases

Y chromosome kits are successfully applied in cases where human biological material exists. With the development of genotyping ability, more Y chromosomal markers are needed for finer identification of male individuals and lineages. In this study, a developmental validation of a newly emerged Y chromosome kit that combines two different kinds of markers: 38 Y-STRs and 3 Y-indels are conducted. The results show that this kit has high sensitivity when there is a small amount of DNA (125 pg), more than one male (minor:major = 1:7), or a mixture of males and females (male:female = 125pg:1875pg), inhibited substances (800 μM hematin and more than 1600 ng/μL humic acid). The kit exhibits high precision level with a standard deviation of allele size no more than 0.14 nt. Locus DYS481 shows the largest stutter rate, with three stutters per true allele. Population samples are well identified (MP of 0.001106), and mutations can be observed in father-son pairs (46 mutations in 70 pairs, 10 in locus DYS627). Out of all the population samples, 13.2% belong to haplogroup M117-O2a2b1a1, with their ethnic group being Han Chinese. The results show that this kit can improve the performance of identifying male individuals, obtaining more unique haplotypes (increasing from 894 to 918 of 1000 male samples) and higher discrimination capacity (increasing from 0.942 to 0.955) in this study compared to previous widely used Yfiler Plus kit. Besides, it gives information about their paternal lineages in forensic genetic casework and genealogical database construction.

Assessment of the forensic application of 50 Y-STR markers in a large pedigree

Short tandem repeats on the Y chromosome (Y-STRs), characterized by paternal inheritance, are valuable in forensic practice. Notably, the potential application of Y-STRs in pedigrees should be drawn upon, especially in China’s surname-concentrated natural villages. The study focused on 50 Y-STRs, including 13 rapidly mutating (RM) Y-STRs that largely constitute the current Y-STR commercial kits, and determined the differences in these Y-STRs between branches in a large pedigree and the discriminatory power of these haplotypes in different units for male relatives. As indicated in the results, 14 inconsistencies were observed at 9 Y-STRs between 10 father-son pairs. In addition, these 50 Y-STR haplotypes discriminated 10 out of 47 father-son pairs, 106 of 148 cousin pairs, 70 of 119 uncle-nephew pairs, 17 of 39 brother pairs, and 14 out of 33 grandfather-grandson pairs in a large pedigree. The RM Y-STR set is able to differentiate close male relatives in a large pedigree.

Assessing 23 Y-STR loci mutation rates in Chinese Han father-son pairs from southwestern China

In this study, we have analyzed 23 Y-chromosomal short tandem repeats (Y-STRs) (DYS576, DYS389I, DYS389II, DYS448, DYS19, DYS391, DYS481, DYS549, DYS533, DYS438, DYS437, DYS570, DYS635, DYS390, DYS439, DYS392, DYS643, DYS393, DYS458, DYS460, DYS385ab, DYS456 and Y-GATA-H4) in 175 father-son sample pairs using a Microreader™ 24Y Direct ID system. Sixteen repeat mutations of father-son pairs at 10 loci, including three mutations at DYS570, 2 mutations at DYS549, DYS460, DYS458, and DYS576, and 1 mutation at other five loci, were revealed. Furthermore, all of the observed repeat mutations were single repeat changes with 5 (31.25%) repeat insertions and 11 (68.75%) repeat deletions. The deletion rate is more than two fold higher than of insertions (11:5 = 2.2-fold). Locus-specific mutation rates estimated varied between 5.71 × 10^-3 (CI from 0.1 × 10^-3 to 31.4 × 10^-3) and 1.71 × 10^-2 (CI from 3.6 × 10^-3 to 49.3 × 10^-3) for the 23 Y-STRs. An average mutation rate across all 23 Y-STR markers was estimated as 3.97 × 10^-3 (CI 2.3 × 10^-3 to 6.4 × 10^-3). Thus, locus-specific mutation rates in DYS460, DYS458, and DYS438, estimated are much higher than previously published comprehensive data, but an average mutation rate across all 23 Y-STR markers is similar to previous reports (3.97 × 10^-3 vs 4.34 × 10^-3). These results by characterizing Y-STR mutations will not only provided new information for Y-STR mutations but also might be important for paternal lineage identification, kinship analysis, and family relationship reconstruction in our forensic Y-STR analysis.

Population genetic data of 4 multicopy Y-STR markers in Chinese

Novel Y chromosomal STR (Y-STR) markers have been continuously discovered during the past decades, promoting the widely application of Y-STRs in the area of forensic science. Here, four multicopy Y-STR markers were focused, including DYF383S1, DYF409S1, DYF411S1 and DYF371, which are rarely reported in China and differ in the number of copies on Y chromosome. Characterization of the markers was performed in population of Hunan province, China, based on sequence analysis. Allele nomenclature and allelic ladder were then developed to avoid the disunity of typing standard. To evaluate their forensic performance, gene diversity of the four loci was investigated in 548 unrelated male individuals from Hunan population. The number of haplotype was analyzed by both conservative (C-type) and expanded approach (E-type) for markers containing more than 2 copies. As detected, there were 7, 9, 13 alleles and 15, 22, 23 haplotypes for DYF383S1, DYF409S1 and DYF411S1, respectively. Thirty-two C-types and 56 E-types were found in DYF371, indicating the highest haplotype diversity (HD) among all tested loci (0.871 and 0.888 for C-type and E-type, respectively). Two other Y-STRs (DYF409S1, DYF411S1) also showed high haplotype diversity (>0.8) in the population. Combining the four loci, discrimination capacity reached 0.505 (C-type) or 0.533 (E-type), and the total HD values exceeded 0.991. The results inferred great potential of the multicopy markers to improve the resolution of paternal identification in China population.

Ethnic fragmentation and degree of urbanization strongly affect the discrimination power of Y-STR haplotypes in central Sahel

Y chromosome short tandem repeats (Y-STRs) are commonly used to identify male lineages for investigative and judicial purposes and could represent the only source of male-specific genetic information from unbalanced female-male mixtures. The Yfiler Plus multiplex, which includes twenty conventional and seven rapidly-mutating Y-STRs, represents the most discriminating patrilineal system commercially available to date. Over the past five years, this multiplex has been used to analyze several Eurasian populations, with a reported discrimination capacity (DC) approaching or corresponding to the highest possible value. However, despite the inclusion of rapidly mutating Y-STRs, extensive haplotype sharing was still reported for some African populations due to a number of different factors affecting the effective population size. In the present study, we analyzed 27 Y-STRs included in the Yfiler Plus multiplex and 82 Y-SNPs in central Sahel (northern Cameroon and western Chad), an African region characterized by a strong ethnic fragmentation and linguistic diversity. We evaluated the effects of population sub-structuring on genetic diversity by stratifying a sample composed of 431 males according to their ethnicity (44 different ethnic groups) and urbanization degree (four villages and four towns). Overall, we observed a low discrimination capacity (DC = 0.90), with 71 subjects (16.5 %) sharing 27 Y-STR haplotypes. Haplotype sharing was essentially limited to subjects with the same binary haplogroup, coming from the same location and belonging to the same ethnic group. Haplotype sharing was much higher in rural areas (average DC = 0.83) than urban settlements (average DC = 0.96) with a significant correlation between DC and census size (r = 0.89; p = 0.003). Notably, we found that genetic differentiation between villages from the same country (Φ_ST = 0.14) largely exceeded that found among countries (Φ_ST = 0.02). These findings have important implications for the choice of the appropriate reference population database to evaluate the statistical relevance of forensic Y-haplotype matches.

Genetic characterisation and forensic importance of 20 Y-STRs in Han population from Anshan, Northeast of China

BACKGROUND

With a population of over 1.4 billion and 56 ethnic groups, China is the largest country in the world in terms of population. Han is the main ethnic group of China (93%).

AIM

To provide genetic data of Y chromosomal STRs from Anshan City, Northeast of China, for the first time, which will serve as a reference database for forensic and population studies.

SUBJECTS AND METHODS

We report data of 20 Y-chromosomal short tandem repeats (YSTRs) genotyped with the Goldeneye^® 20Y kit in 270 Han individuals residing in Anshan City of China.

RESULTS

A total of 170 alleles were observed on 20 Y-STRs. The gene diversities varied from 0.3460 (DYS391) to 0.9692 (DYS385). Overall haplotype diversity was almost 1 with 261 unique haplotypes, while the discrimination capacity (DC) was 0.9814. Pairwise Rst and Fst genetic analyses, MDS plot, N-J tree and PCA showed the genetic structure of Anshan Han population was significantly different from other minority groups like Tibetans and Kazakhs.

CONCLUSIONS

Results of this study showed that Goldeneye^® 20Y system loci have strong discriminatory power in the Anshan Han population of China which makes this kit suitable for forensic applications in this ethnic group.

Geographical structuring and low diversity of paternal lineages in Bahrain shown by analysis of 27 Y-STRs

We have determined the distribution of Y-chromosomal haplotypes and predicted haplogroups in the ethnically diverse Kingdom of Bahrain, a small archipelago in the Arabian Gulf. Paternal population structure within Bahrain was investigated using the 27 Y-STRs (short tandem repeats) in the Yfiler Plus kit to generate haplotypes from 562 unrelated Bahraini males, sub-divided into four geographical regions—Northern, Capital, Southern and Muharraq. Yfiler Plus provided a significant improvement over the 17-locus Yfiler kit in discrimination capacity (from 77% to 87.5% overall), but discrimination capacity differed widely between regions from 98.4% in Muharraq to 75.2% in the Northern region, an unusually low value possibly resulting from recent rapid population expansion. Clusters of closely related male lineages were seen, with only 79.4% of donors displaying unique haplotypes and 59% of instances of shared haplotypes occurring within, rather than between, regions. Haplogroup prediction indicated diverse origins of the population with a predominance of haplogroups J2 and J1, both typical of the Arabian Peninsula, but also haplogroups such as B2 and E1b1a likely originating in Africa, and H, L and R2 likely indicative of migration from South Asia. Haplogroup frequencies differed significantly between regions, with J2 significantly more common in the Northern region compared with the Southern, possibly due to differential settlement by Baharna and Arabs. Our study shows that paternal lineage population structure can exist even over small geographical scales, and that highly discriminating genetic tools are required where rapid expansions have occurred within tightly bounded populations.

Technical note: developmental validation of a novel 41-plex Y-STR system for the direct amplification of reference samples

The SureID^® PathFinder Plus is a new 6-dye, 41-plex Y-STR system that includes the 17 loci from the Yfiler^® kit (DYS19, DYS385a/b, DYS389I/II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4) plus 14 rapidly mutating Y-STR loci (DYS449, DYS481, DYS518, DYS527a/b, DYS533, DYS549, DYS570, DYS576, DYS627, DYF387S1a/b, and DYF404S1), and 10 low-medium mutation loci (DYS388, DYS444, DYS447, DYS460, DYS522, DYS557, DYS593, DYS596, DYS643, and DYS645). The inclusion of the 14 rapidly mutating Y-STR loci improves the discrimination of related individuals. Conversely, the 10 low-medium mutation loci are suitable not only for familial searching but also for providing a higher refinement in the construction of Y chromosome phylogenetic relationships among lineages. The 41-plex Y-STR system is designed for direct amplification of reference samples, such as blood samples on an FTA^® Card, gauze, tissue, or cotton substrates as well as hair root or buccal samples on swabs. We performed developmental validation work including accuracy, stability, stutter precision, species specificity, sensitivity, PCR inhibitors, reproducibility, parallel testing of the system, and suitability for use on DNA mixtures. In addition, mutations of the loci were analyzed by 754 DNA-confirmed father-son pairs. The results demonstrate that this kit, developed in-house, is time-efficient, accurate, reliable, and highly informative for forensic database, familial searching, and distinguishing related males.