Genetic analysis of Southern Brazil subjects using the PowerSeq™ AUTO/Y system for short tandem repeat sequencing

With the advent of Next-Generation Sequencing technology, sequencing of short tandem repeats (STRs) allows for a more detailed analysis when compared to size-based fragment methods (capillary electrophoresis-CE). The implementation of high-throughput sequencing can help uncover deeper genetic diversities of different populations. Subjects from the South region of Brazil present a particular and more homogeneous ancestry background when compared to other regions of the country. Both autosomal and Y- STRs have been analyzed in these individuals; however, all analyses published to date encompass data from CE-based fragment analysis. In this study, a genetic analysis of 59 individuals from Southern Brazil was performed on STR sequences. Forensically relevant STRs were PCR-enriched using a prototype of the PowerSeq™ AUTO/Y system (Promega Corp.). Next-generation sequencing was performed on an Illumina MiSeq instrument. The raw data (FASTQ files) were processed using a custom designed sequence processing tool, Altius. Isoalleles, which are sequence-based allelic variants that do not differ in length, were observed in nine autosomal and in six Y- STRs from the core global forensic marker set. The number of distinctive alleles based on sequence was higher when compared to those based on length, 37.3% higher in autosomal STRs and 13.8% higher in Y-STRs. The most polymorphic autosomal locus was D12S391, which presented 38 different sequence-based alleles. Among the loci in the Y chromosome, DYS389II presented the highest number of isoalleles. In comparison to CE analysis, Observed and Expected Heterozygosity, Polymorphic Information Content (PIC) and Genetic Diversity also presented higher values when the alleles were analyzed based on their sequence. For autosomal loci, Polymorphic Information Content (PIC) was 2.6% higher for sequence-based data. Diversity was 9.3% and 6.5% higher for autosomal and Y markers, respectively. In the analysis of the repeat structures for the STR loci, a new allele variant was found for allele 18 in the vWA locus. The STR flanking regions were also further investigated and sixteen variations were observed at nine autosomal STR loci and one Y-STR locus. The results obtained in this study demonstrate the importance of genetic analysis based on sequencing and highlight the diversity of the South Brazilian population when characterized by STR sequencing.