A posteriori parameters from paternity tests of a Mexican laboratory with the powerplex fusion system

Abstract

Population studies regarding Human identification (HID) systems report a priori forensic parameters, but rarely they describe a posteriori parameters from concluded paternity tests. We analyzed data from the PowerPlex® Fusion System in 1503 paternity tests from a Mexican laboratory for five years (2016–2020). The motherless duo paternity tests (89.8%) were more frequent than the standard trio tests (10.2%). A notable increase in motherless tests was noted regarding our previous report (89.8% vs 77.3%), probably explained by the COVID-19 pandemic. The estimated exclusion frequency in Mexico ranged from 30.1 (trio) to 32.1% (duo). For paternity exclusions, we report the number of mismatches and the frequency at which each STR was involved. The PowerPlex® Fusion system showed more than five mismatches in 100% of the standard trio tests excluding paternity, and the majority of motherless-duo tests (98.1%). In positive paternity tests, PowerPlex® Fusion offered a higher combined paternity index (PI) (average 1.18 E + 10) regarding HID systems with 15 and 20 STRs, even without the inclusion of the Y-linked locus DYS391 to the kinship interpretation. Individual and global STR mutation rates were estimated from 17 paternal mutations (μ = 0.0017), the majority involving a single-step mutation (94.11%). Five independent null alleles were detected, most of them involving the Penta E locus (80%), which suggests caution to the users working with DNA databases or kinship analysis, to avoid false exclusions with Penta E. In brief, our results provide a better overview of a posteriori informativeness offered by the PowerPlex® Fusion system for paternity testing in Mexico.