A Y-chromosome STR Marker Should Be Added to Commercial Multiplex STR Kits

Nanopore sequencing of forensic short tandem repeats using QNome of Qitan Technology

Devices of nanopore sequencing can be highly portable and of low cost. Thus, nanopore sequencing is promising in in-field forensic applications. Previous investigations have demonstrated that nanopore sequencing is feasible for genotyping forensic short tandem repeats (STRs) by using sequencers of Oxford Nanopore Technologies. Recently, Qitan Technology launched a new portable nanopore sequencer and became the second supplier in the world. Here, for the first time, we assess the QNome (QNome-3841) for its accuracy in nanopore sequencing of STRs and compare with MinION (MinION Mk1B). We profile 54 STRs of 21 unrelated individuals and 2800M standard DNA. The overall accuracy for diploid STRs and haploid STRs were 53.5% (378 of 706) and 82.7% (134 of 162), respectively, by using QNome. The accuracies were remarkably lower than those of MinION (diploid STRs, 84.5%; haploid, 90.7%), with a similar amount of sequencing data and identical bioinformatics analysis. Although it was not reliable for diploid STRs typing by using QNome, the haploid STRs were consistently correctly typed. The majority of errors (58.8%) in QNome-based STR typing were one-repeat deviations of repeat units in the error from true allele, related with homopolymers in repeats of STRs.

Developmental validation of GlobalFiler™ PCR amplification kit: a 6-dye multiplex assay designed for amplification of casework samples

The GlobalFiler™ PCR Amplification Kit is a single multiplex assay that amplifies a set of 24 markers, which encompass the European Standard Set and CODIS (Combined DNA Index System) recommended composite set of loci. In addition to more loci and a 6-dye chemistry format, the Master Mix has been formulated to allow higher sample loading volume for trace DNA samples. The GlobalFiler™ Kit has been optimized to deliver high performance on casework samples, while also delivering fast thermal cycling, with an amplification time of approximately 80 min. Here, we report the results of the developmental validation study which followed the SWGDAM (Scientific Working Group on DNA Analysis Methods) guidelines and includes data for PCR-based studies, sensitivity, species specificity, stability, precision, reproducibility and repeatability, concordance, stutter, DNA mixtures, and performance on mock casework samples. The results validate the multiplex design as well as demonstrate the kit's robustness, reliability, and suitability as an assay for human identification with casework DNA samples.

"YFlag"--a single-base extension primer based method for gender determination

Assigning the gender of a DNA contributor in forensic analysis is typically achieved using the amelogenin test. Occasionally, this test produces false-positive results due to deletions occurring on the Y chromosome. Here, a four-marker "YFlag" method is presented to infer gender using single-base extension primers to flag the presence (or absence) of Y-chromosome DNA within a sample to supplement forensic STR profiling. This method offers built-in redundancy, with a single marker being sufficient to detect the presence of male DNA. In a study using 30 male and 30 female individuals, detection of male DNA was achieved with c. 0.03 ng of male DNA. All four markers were present in male/female mixture samples despite the presence of excessive female DNA. In summary, the YFlag system offers a method that is reproducible, specific, and sensitive, making it suitable for forensic use to detect male DNA.