In many societies worldwide, surnames are transmitted through the paternal line, in a similar fashion to the Y chromosome. This parallel mode of inheritance for surnames and Y DNA creates a link that can be exploited in a forensic context to generate investigative leads. Specifically, Y-STR profiles obtained from unknown male DNA may be used to infer probable surnames, thereby narrowing the pool of potential suspects when traditional investigative methods have been exhausted.  

The development and application of a large-scale Y-STR and surname database for forensic casework will be presented. The assembled database comprises more than 200 000 Y-STR profiles associated with surnames of diverse biogeographical origins. A simple yet robust scoring formula was developed to rank database candidates based on their degree of similarity to the unknown profile. The score reflects the number of shared alleles while applying penalties for mismatched loci. The penalties are weighted according to locus-specific mutation rates, and the number of steps between alleles. 

A validation study was conducted using Y-STR profiles with known self-reported surnames. Using the database and scoring formula, the correct surname was ranked among the top candidates for over 50% of tested profiles. These results demonstrate the practical utility of the method despite inherent limitations such as non-paternity events or surname changes. 

Finally, forensic cases will be presented in which this approach proved instrumental in case resolution. The synergy between a Y-surname search and investigative genetic genealogy (IGG) will be discussed; how it allows to target relevant paternal lineages, resulting in a more time-efficient investigation. Overall, the surname search using Y-STR profiles can help solve cases, is cost-effective, rapid, and relies on technologies already implemented in most forensic laboratories. 

Authors

• Valérie Clermont-Beaudoin (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada) 
• Sarah Noël (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada) 
• Jean-François Lefebvre (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada) 
• Isabelle Bachand (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada) 
• Josée Noël (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada) 
• Sarah Bourgoin (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada) 
• Diane Séguin (Laboratoire de sciences judiciaires et médecine légale (LSJML), Canada)