Forensic analysis of autosomal STR markers using Pyrosequencing

Abstract 

Short tandem repeats (STRs) are highly variable, and therefore routinely used in forensic investigations for a DNA-based individual identification. The routine assay is commonly performed by size separation using capillary electrophoresis, but alternative technologies can also be used. In this study, a Pyrosequencing assay was developed for analysis of STR markers useful in forensic DNA analysis. The assay was evaluated for 10 different STR loci (CSF1PO, TH01, TPOX, D3S1358, D5S818, D7S820, D8S1179, D13S317, D16S539 and Penta E) and a total of 114 Swedish individuals were genotyped. This genotyping strategy reveal the actual sequence and variant alleles were seen at several loci, providing additional information compared to fragment size analysis. At the D13S317 locus a T/A SNP located in the last repeat unit was observed in 92% of the genotypes. Moreover, an upstream flanking SNP at locus D7S820, a SNP within the repeats at D3S1358 and D8S1179 and a deletion in the flanking region at locus D5S818 were observed. The Pyrosequencing method was first developed for SNP typing and sequencing of shorter DNA fragments but the method also provides an alternative method for STR analysis of less complex repeats. This assay is suitable for investigation of new markers, a rapid compilation of population data and for confirmation of variant and new alleles.

Keywords: Pyrosequencing, STR, Sequence-directed nucleotide addition, Forensic identification