With the increasing sensitivity of DNA analytical methods, higher-order mixtures (with four, five, or six contributors) are being detected more frequently during the analysis of touched objects. As probabilistic genotyping systems now enable the interpretation of such complex DNA profiles, there is growing interest among forensic laboratories in evaluating their evidential value. According to the DNAmix 2021 study (Hicklin et al., 2023), many laboratories routinely interpret mixtures containing up to four contributors, while approximately 15% extend their analyses to mixtures with as many as five contributors.

In this study, we assess the informative value of five-contributor DNA mixtures and their interpretation using the STRmix probabilistic genotyping system. Our results demonstrate that both sensitivity and specificity for these highly complex mixtures are comparable to those observed in less complex mixtures, indicating that they can be reliably interpreted using this approach. Additionally, the study examines six-contributor mixtures and highlights key limitations that may impact their interpretation. These findings provide valuable insights into the capabilities and constraints of probabilistic genotyping when applied to increasingly complex DNA evidence.

Authors

• Josee Noel (Laboratoire de sciences judiciaires et de médecine légale, Canada)
• Sarah Noel (Laboratoire de sciences judiciaires et de médecine légale, Canada)
• Dominic Granger (Laboratoire de sciences judiciaires et de médecine légale, Canada)
• Thibault de Malliard (Laboratoire de sciences judiciaires et de médecine légale, Canada)
• Diane Séguin (Laboratoire de sciences judiciaires et de médecine légale, Canada)