Characterization of 58 STRs and 94 SNPs with the ForenSeq™ DNA signature prep kit in Mexican-Mestizos from the Monterrey city (Northeast, Mexico)

Past, Present and Future Perspectives of Forensic Genetics

Forensic genetics has experienced remarkable advancements over the past decades, evolving from the analysis of a limited number of DNA segments to comprehensive genome-wide investigations. This progression has significantly improved the ability to establish genetic profiles under diverse conditions and scenarios. Beyond individual identification, forensic genetics now enables the inference of physical traits (e.g., eye, hair, and skin color, as well as body composition), biogeographic ancestry, lifestyle habits such as alcohol and tobacco use, and even the transfer of genital microbiomes post-coitus, among other characteristics. Emerging trends point to a future shaped by the integration of cutting-edge technologies, including CRISPR-Cas systems, artificial intelligence, and machine learning, which promise to further revolutionize the field. This review provides a thorough exploration of forensic genetics, tracing its evolution from its foundational methods (past) to its diverse modern applications (present) and offering insights into its potential future directions.

Choice between DNA primer sets (A or B) of the ForenSeq kit: forensic evaluation in a Mexican admixed population sample

Massively parallel sequencing (MPS) overcomes many PCR-CE limitations to analyze STRs and allow simultaneous inclusion of SNPs in forensic cases. By MPS, the ForenSeq™ DNA Signature Prep kit analyzes 27 aSTRs, 7 X-STRs, 24Y-STRs, and 94 identity-informative SNPs (iiSNPs) with the DNA Primer Set-A (DPS-A). Optionally, the DNA Primer Set-B (DPS-B) adds to the analysis 56 ancestry-informative SNPs (aiSNPs) and 24 phenotype-informative SNPs (piSNPs), but diminishes from 96 to 32 the number of samples per sequencing run. We assessed the forensic informativity provided by the loci analyzed by these two DPS in admixed individuals from Mexico City (Center, Mexico). For STRs, we report length-based (LB) and sequence-based (SB) allele frequencies and forensic parameters of the 152 identity informative markers (DPS-A). For aSTRs, the combined PD of SB genotypes (PD ~ 100%) was ~ 2949 times larger than that from LB. Conversely, the observed phenotype distribution offered low PD levels (PD = 6.6% and 10.4%), whereas piSNPs predicted accurately only the modal brown eye and dark hair colors, respectively. Similarly, aiSNPs detected a large prevalence of admixed individuals (97.3%; PD = 5.4%). Although few individuals were inferred as Europeans and Native Americans (1.37% each), they were self-declared as admixed, which result confusing for HID purposes. In brief, SB genotypes increased significantly the informativity of STRs to solve complex cases (DPS-A), whereas aiSNPs and piSNPs added mostly irrelevant information (DPS-B). We provide useful cost-benefit criteria in one Latin American population to choose DPS-A (96 samples) instead of DPS-B (32 samples) of the Forenseq kit.

Sequence-based genotyping of 58 STRs and 94 iiSNPs with Verogen's ForenSeq DNA signature prep kit in Mexican-Mestizos from Jalisco state (West, México)

Massively parallel sequencing (MPS) allows simultaneous detection of sequence variation of both Single nucleotide polymorphisms (SNPs) and Short tandem repeats (STRs) with different inheritance patterns, such as autosomal (aSTRs), patrilineal Y-linked (Y-STRs), and X-chromosomal (X-STRs). However, to apply these methodologies for Human Identification (HID), population databases with sequence-based (SB) allele frequencies are needed. For this reason, we sequenced 58 STRs (aSTRs, X-STRs, and Y-STRs) and 94 identity informative SNPs (iiSNPs) on 95 Mexican-Mestizo (admixed) individuals from the Jalisco state (West, Mexico), with the Primer Set-A of the ForenSeq™ DNA Signature Prep Kit. For SB allele calling, we used the recent ISFG recommendations for STR sequence nomenclature. The information provided by the SB variation (including flanking regions) in the STRs increased their allelic diversity regarding the length-based (LB) alleles, as follows: 46.2%, 47%, and 18.4% for aSTRs, X-STRs, and Y-STRs, respectively. The combined power of discrimination for aSTRs was virtually 100% based on LB and SB alleles, whereas the combined power of exclusion was 99.9999999977% and 99.9999999999%, respectively. The haplotypes based on X-STRs and Y-STRs show 100% of discriminatory capacity. Our results showed an increase in allele diversity and discriminatory capacity of this genomic system regarding forensic kits based on capillary electrophoresis. This study represents an effort to incorporate more genomic databases from Mexico and Latin America for the forensic application of MPS.

Enhancing the Potential of Microhaplotypes for Forensic Applications: Insights from Afghan and Somali Populations

Microhaplotypes (MHs) are a novel class of genetic markers, exhibiting features that position them as an alternative to STRs and SNPs in addressing challenges commonly encountered in forensic investigations. Additionally, MHs can also offer valuable insights for ancestry inference. However, due to the novelty of MHs, extensive research in different global populations is required before implementation in forensic casework and general research. In this study, individuals from Afghanistan and Somalia were characterized with the Ion AmpliSeq™ MH-74 Plex Research Panel previously developed for forensic genetic purposes. A total of 84 Afghan and 89 Somalian samples were sequenced on the Ion GeneStudio™ S5 System. This led to the identification of 32 and 42 single nucleotide variants in the Afghan and Somalian populations, respectively, that were not included in the former MH definitions. Most of the observed variants were considered to be rare occurrences, being observed one or two times in the dataset. The average values of the effective number of alleles (Ae) were 3.7 for Somalia and 3.6 for Afghanistan-pointing to elevated intrapopulation diversities compared to Europeans. Other parameters (Ho, He, PIC, PD, and PE) consistently showed higher average values in the Afghans and Somalis compared to the previously studied populations. PCA and STRUCTURE analyses with 1000 Genomes samples assigned the Somalis to a different cluster than the other sub-Saharan African populations. The analyses also showed higher European and East Asian co-ancestry in the Afghans than in the remaining South Asian populations. The capability of the MH-74 plex to address common kinship problems was evaluated through computational simulations, considering generic thresholds differing by one order of magnitude to assess the FDRs. The median LR > 1013 for true siblings when the hypotheses 'full siblings' and 'unrelated individuals' were compared. As expected, the median LRs were much lower for simulated half-siblings and cousins. This work evaluated the forensic potential of MHs in understudied populations. Overall, the studied panel was versatile and capable of being applied in different forensic applications.

Genetic Diversity and Forensic Parameters of 27 Y-STRs in Two Mestizo Populations from Western Mexico

BACKGROUND

Analyzing Y-chromosome short tandem repeats (Y-STRs) is essential in forensic genetics and population studies. The Yfiler™ Plus kit, which includes 27 Y-STR markers, enhances the discrimination power for forensic and kinship applications. However, this genetic system has not been analyzed in Mexican populations, which limits its application and representativeness in international databases.

OBJECTIVES

We wished to examine the genetic diversity and forensic parameters of the 27 Y-STRs included in the YFiler™ Plus kit in two populations from Western Mexico (Jalisco and Michoacán).

METHODS

Male DNA samples were amplified using the Yfiler™ Plus kit, followed by a fragment analysis via capillary electrophoresis (CE). The haplotype frequencies and forensic parameters were calculated. The haplogroups of all samples were predicted, and the distribution and percentages of ancestries were determined. The Rst genetic distances, including reference populations, were calculated and graphically represented in a multidimensional scaling (MDS) plot.

RESULTS

A total of 224 haplotypes were identified in all of the samples, of which 98.66% corresponded to unique haplotypes. Bi- and tri-allelic patterns were observed in both populations. The observed discriminatory capacity was 98.4% for Jalisco and 98.9% for Michoacán, while the haplotype diversity values were 0.9998 and 0.9997, respectively. The most frequent haplogroup was R1b, followed by Q, representing the European and Native American ancestries, in both populations.

CONCLUSIONS

This study is the first to report the haplotype diversity and forensic parameters of the 27 Y-STRs included in the Yfiler™ Plus kit in Mexican populations. These findings confirm the forensic utility of these markers for human identification, biological relationship testing, and criminal investigations, reinforcing their applicability in forensic casework.

Characterisation of identity-informative genetic markers in the Australian population with European ancestry

Identity-informative single nucleotide polymorphisms (iiSNPs) are valuable genetic markers for human identification and kinship testing in forensic casework, especially when the quality and quantity of DNA evidence is not suitable for routine short tandem repeat (STR) profiling. This study analysed 105 buccal samples representing the Australian population with European ancestry in order to assign allele frequencies and conduct population genetic analyses for 94 iiSNPs and 20 STRs. The markers were assessed by calculating relevant forensic statistics and testing for deviations from Hardy-Weinberg and linkage equilibrium. No linkage of statistical significance was observed between any of the pair-wise combinations of the combined 114 identity-informative markers and only one STR exhibited deviation from Hardy-Weinberg equilibrium (D8S1179). The probability of matching genotypes being observed within this population was of the order of 10-23 for STRs, 10-38 for iiSNPs and 10-60 for the combined identity-informative marker panel, improving the ability to discriminate between individuals when calculating likelihood ratios in direct or indirect matching scenarios. Further, the addition of iiSNPs will facilitate identifications when suboptimal STR profiles are recovered from compromised or challenging samples and aid comparisons to genetic relatives for familial or kinship testing.

Applications and Performance of Precision ID GlobalFiler NGS STR, Identity, and Ancestry Panels in Forensic Genetics

Short Tandem Repeat (STR) testing via capillary electrophoresis is undoubtedly the most popular forensic genetic testing method. However, its low multiplexing capabilities and limited performance with challenging samples are among the factors pushing scientists towards new technologies. Next-generation sequencing (NGS) methods overcome some of these limitations while also enabling the testing of Single-Nucleotide Polymorphisms (SNPs). Nonetheless, these methods are still under optimization, and their adoption into practice is limited. Among the available kits, Thermo Fisher Scientific (Waltham, MA, USA) produces three Precision ID Panels: GlobalFiler NGS STR, Identity, and Ancestry. A clear review of these kits, providing information useful for the promotion of their use, is, however, lacking. To close the gap, a literature review was performed to investigate the popularity, applications, and performance of these kits. Following the PRISMA guidelines, 89 publications produced since 2015 were identified. China was the most active country in the field, and the Identity Panel was the most researched. All kits appeared robust and useful for low-quality and low-quantity samples, while performance with mixtures varied. The need for more population data was highlighted, as well as further research surrounding variables affecting the quality of the sequencing results.

Performance and characterization of 94 identity-informative SNPs in Northern Han Chinese using ForenSeq ™ DNA signature prep kit

Target and flanking region (FR) variation at 94 identity-informative SNPs (iSNPs) are investigated in 635 Northern Han Chinese using the ForenSeq DNA Signature Prep Kit on the MiSeq FGx Forensic Genomics System. The dataset presents the following performance characteristics (average values): ≥60% bases with a quality score of 20 or higher (%≥ Q20); >700 × of depth of coverage (DoC) from both Sample Details Reports and Flanking Region Reports; >80% of effective reads; ≥60% of allele coverage ratio (ACR); and ≥70% of inter-locus balance, while some stable low-performance characteristics are also observed: low DoC at rs1736442, rs1031825, rs7041158, rs338882, rs2920816, rs1493232, rs719366, and rs2342747; high noise at rs891700; and imbalanced ACR at rs6955448 and rs338882. The average amplicon length is 69 bp, suitable for detecting degraded samples. Bioinformatic concordance achieves 99.99% between the ForenSeq Universal Analysis Software (UAS) and the Integrative Genomic Viewer (IGV) inspection. Discordance results from flanking region deletions of rs10776839, rs8078417, rs2831700, and rs1454361. Due to FR variants within amplicons detected by massively parallel sequencing (MPS), the increases in the number of unique alleles, effective alleles (Ae), and observed heterozygosity (Hobs) are 46.81%, 4.51%, and 3.29%, respectively. Twelve FR variants are first reported to dbSNP, such as rs1252699848, rs1665500714, rs1771121532, rs2097285015, rs1851671415, rs2045669877, rs2046758811, rs2044248635, rs1251308240, rs1968822112, rs1981638299, and rs1341756746. All 94 iSNPs from target and amplicon data are in Hardy-Weinberg equilibrium (HWE) and independent within autosomes. As expected, forensic parameters from the amplicon data increase significantly on the combined power of discrimination (CPD = 1 - 3.9876 × 10-38) and the combined power of exclusion (CPE = 1 - 6.6690 × 10-8). Additionally, the power of the system effectiveness (CPD = 1 - 6.7054 × 10-72 and CPE = 1 - 4.4719 × 10-20) with sequence-based 27 autosomal STRs and 94 iSNP amplicons in combination is substantially improved compared to one type of marker alone. In conclusion, we have established a traditional length-based and current sequence-based reference database with 58 STRs and 94 iSNPs in the Northern Han Chinese population. We hope these data can serve as a solid reference and foundation for forensic practice.