A substantially lower frequency of uninformative matches between 23 versus 17 Y-STR haplotypes in north Western Europe

The analysis of human short tandem repeats of the Y-chromosome (Y-STRs) provides a powerful tool in forensic cases for male sex identification, male lineage identification and identification of the geographical origin of male lineages. As the commonly used 12 and 17 Y-STR multiplexes do not discriminate between some unrelated males, additional Y-STRs were implemented in the PowerPlex(®) Y23 System to supplement the existing commercial Y-STR kits. Until today, the forensic value of a (near) 23 versus 17 Y-STR haplotype match between an unknown DNA donor and a certain biological sample in a database is not yet well studied. This will be of huge interest for cases where an autosomal DNA profile yields no match to a DNA database and the database is used for familial searching (male relative(s) of the offender) or for the estimation of the geographical origin of the offender. In order to value (near) 23 Y-STR haplotype matches in a local sample from Western Europe, we selected the region of Flanders (Belgium) due to the already present knowledge on its Y-chromosomal variants. Many Y-chromosomes of this region were previously genotyped with Y-SNPs at a high resolution of the most recently updated Y-chromosomal tree and the deep-rooted genealogy of each DNA donor was already established. By comparing (near) matches of 23 versus 17 Y-STR haplotypes between patrilineal-unrelated males, a substantial lower number of uninformative (near) 23 Y-STR haplotype matches has been observed compared to 17 Y-STR haplotypes. Furthermore, the use of SNP data was informative to discriminate >60% of unrelated males with an (near) identical 17 Y-STR match while SNP data was only necessary to discriminate about 10% of unrelated males with a 23 Y-STR haplotype that differed at only two Y-STRs. This shows the higher value of the Y23 haplotype within familial DNA searching and the estimation of the geographical origin of a DNA donor. Therefore, the use of the PowerPlex(®) Y23 System instead of the commonly used 12 and 17 Y-STRs by the forensic community is recommended as it will increase the efficiency of Y-STRs in forensic casework.