Improved specificity of Y-STR typing in DNA mixture samples

Y-STR loci are beneficial for the analysis of forensic samples especially in sexual assault cases or other situations where mixtures of male and female cells are present. However, the amplification of Y-chromosomal STRs is also known to result in the formation of artefactual amplification products, mainly due to insufficient PCR specificity. This is a major drawback of the method, as the sensitivity as well as the correct Y-STR interpretation are affected. In our study, the addition of a PCR enhancer to the reaction master-mix resulted in a significant increase of specificity of Y-STR typing. This was clearly demonstrated by a loss of artefactual signal with increasing enhancer concentration, while the peak heights of the Y-STR alleles were not significantly affected by the enhancer. Mixtures of up to 1:500 (200 pg male and 100 ng female DNA) gave correct Y-STR profiles when the PCR enhancer was added to the reaction, while artefactual amplification succeeded over Y-specific amplification when no PCR enhancer was present.