Forensic assessment on the application of a virtual pool of 30 Y-STRs

Ideally, a panel of Y short tandem repeats (Y-STRs) should include markers with gene diversity (GD) ≥ 0.70 to guarantee a highly accurate and precise individual identification in all forensic situations where Y loci analysis is necessary to support the findings obtained with autosomal STRs. Since not all markers in a multiplex set reach the optimal GD value, to achieve a greater discrimination capacity (DC), the number of Y-STRs has been grad ually expanded also with the addition of rapidly mutating Y-STRs (RM Y-STRs). The present study has tried to assess, based on the genetic diversity of each Y-STR and the cumulative haplotype diversity provided by the single Y-STR panels tested, whether to increase in the number of Y-STRs is effective. For this purpose, three commercially available forensic kits - the PowerPlex® Y23 System, the Yfiler™ Plus PCR Amplification Kit, and the ForenSeq™ DNA Signature Prep Kit - that allow for the simultaneous analysis of 22–25 Y chromosome markers (including Y-STRs and RM Y-STRs) have been used for typing 115 unrelated male individuals from North-East Italy employing two capillary electrophoresis (Applied Biosystems® 3130 Genetic Analyzer and SeqStudio Genetic Analyzer for HID) and one massively parallel sequencing (MiSeq FGx™ Forensic Genomics System) systems. Forensic parameters, such as gene diversity, cumulative haplotype diversity (cHD), and discrimination capacity, were determined for the three Y-STRs kits and the virtual pool of 30 Y-STRs obtained by the overall combination of the Y-loci of the three kits. From the findings, it emerges that twelve markers in the virtual panel of 30 Y-STRs, are characterized by a value of GD ≥ 0.70, and of these, eleven included in the Yfiler™ Plus kit seem to be sufficient to ensure the achievement of haplotype resolution. In light of this, it does not appear necessary to expand the number of Y-STRs in the currently available kits.