Forensic and genetic characterizations of diverse southern Thai populations based on 15 autosomal STRs

Southern Thailand is home to various populations; the Moklen, Moken and Urak Lawoi’ sea nomads and Maniq negrito are the minority, while the southern Thai groups (Buddhist and Muslim) are the majority. Although previous studies have generated forensic STR dataset for major groups, such data of the southern Thai minority have not been included; here we generated a regional forensic database of southern Thailand. We newly genotyped common 15 autosomal STRs in 184 unrelated southern Thais, including all minorities and majorities. When combined with previously published data of major southern Thais, this provides a total of 334 southern Thai samples. The forensic parameter results show appropriate values for personal identification and paternity testing; the probability of excluding paternity is 0.99999622, and the combined discrimination power is 0.999999999999999. Probably driven by genetic drift and/or isolation with small census size, we found genetic distinction of the Maniq and sea nomads from the major groups, which were closer to the Malay and central Thais than the other Thai groups. The allelic frequency results can strength the regional forensic database in southern Thailand and also provide useful information for anthropological perspective.

Genetic polymorphism of 19 autosomal STR loci in the Yi ethnic minority of Liangshan Yi autonomous prefecture from Sichuan province in China

The Yi is one of fifty-six ethnic populations and one of the most ancient ethnic groups in China. The Liangshan Yi Autonomous Prefecture (LYAP) in Sichuan Province has the single largest Yi community in China. To establish a Yi population database in the LYAP of Sichuan in China, a Goldeneye™ DNA Identification System 20A Kit with 19 autosomal STRs (short tandem repeats) was used. As a result, the total discrimination power (TDP) and the cumulative probability of exclusion (CPE) for these STRs in 1016 unrelated individuals were 0.999999999999999999999897 and 0.9999999597, respectively. Totals of 273 alleles for 19 STRs and 8–22 alleles for each locus were found. The allelic frequencies ranged from 0.0005 to 0.5084. The forensic parameter averages of these STRs were as follows: observed heterozygosity (Hobs) of 78.44%, expected heterozygosity (Hexp) of 79.89%, discrimination power (DP) of 92.66%, and probability of exclusion (PE) of 57.68%. Penta E presented the highest levels of Hobs and DP, whereas TPOX showed the lowest Hobs and DP values. Nei’s standard genetic distance matrix among 31 populations found that the nearest genetic distance to the Yi population was the Sichuan Han (0.0056). Altogether, we first reported the forensic parameters and allele frequencies of 19 autosomal STRs of the Yi group in Liangshan. These 19 STR makers could provide highly informative polymorphisms for individual identification, paternity testing and genetic population analyses.

Accurate profiling of forensic autosomal STRs using the Oxford Nanopore Technologies MinION device

The high variability characteristic of short tandem repeat (STR) markers is harnessed for human identification in forensic genetic analyses. Despite the power and reliability of current typing techniques, sequence-level information both within and around STRs are masked in the length-based profiles generated. Forensic STR typing using next generation sequencing (NGS) has therefore gained attention as an alternative to traditional capillary electrophoresis (CE) approaches. In this proof-of-principle study, we evaluate the forensic applicability of the newest and smallest NGS platform available — the Oxford Nanopore Technologies (ONT) MinION device. Although nanopore sequencing on the handheld MinION offers numerous advantages, including on-site sample processing, the relatively high error rate and lack of forensic-specific analysis software has prevented accurate profiling across STR panels in previous studies. Here we present STRspy, a streamlined method capable of producing length- and sequence-based STR allele designations from noisy, long-read data. To demonstrate the capabilities of STRspy, seven reference samples (female: n = 2; male: n = 5) were amplified at 15 and 30 PCR cycles using the Promega PowerSeq 46GY System and sequenced on the ONT MinION device in triplicate. Basecalled reads were processed with STRspy using a custom database containing alleles reported in the STRSeq BioProject NIST 1036 dataset. Resultant STR allele designations and flanking region single nucleotide polymorphism (SNP) calls were compared to the manufacturer-validated genotypes for each sample. STRspy generated robust and reliable genotypes across all autosomal STR loci amplified with 30 PCR cycles, achieving 100% concordance based on both length and sequence. Furthermore, we were able to identify flanking region SNPs with >90% accuracy. These results demonstrate that nanopore sequencing platforms are capable of revealing additional variation in and around STR loci depending on read coverage. As the first long-read platform-specific method to successfully profile the entire panel of autosomal STRs amplified by a commercially available multiplex, STRspy significantly increases the feasibility of nanopore sequencing in forensic applications.