Validation of Y-ancestor time calculators for forensic familial searching

When no suspects are identified in a forensic case as the donor of a biological trace, familial searching through the Y-chromosome can be used as an identification method to find paternally related males of the perpetrator. When a close Y-haplotype match is identified, the time to their most recent common ancestor (tMRCA) can be estimated to reconstruct their genealogy. To date, three online tMRCA calculators (McDonald, Walker and McGee) exist based on the infinite alleles model (IAM), but were not yet validated. In this study, the calculators were investigated using our genetic-genealogy database containing 1,126 genealogical pairs with known tMRCA, in which 42 Y-STR markers were analyzed. We observed that the McGee calculator is very discordant with our dataset, while the others give quite similar results. Overall, the tMRCAs from our genealogical pairs are located within the 95% CI, but are slightly underestimated for pairs with a close Y-haplotype match, and overestimated when more Y-STR differences are present. Additionally, their large 95% CI are not appropriate for genealogy reconstruction for forensic purposes. To further improve tMRCA estimations, individual Y-STR mutation rates and allele calls should be included to take hidden Y-STR differences into account.status: Published onlin