Population data of 23 STR loci (PowerPlex® Fusion System) in Mexican Mestizos from the West Region.

We analyzed 238 unrelated Mestizo (admixed) individuals from the West region of Mexico with the PowerPlex® Fusion System (Promega Corp.). Allele frequencies and forensic parameters were estimated for the 23 STRs included in this kit. Hardy-Weinberg equilibrium by locus and non-association between pair of loci were demonstrated by exact tests in this population. The combined PE and PD offered by this HID kit were ≥0.9999999986, representing a substantial improvement with respect to those previously offered by 15 STR systems. Interpopulation comparison by AMOVA tests demonstrated low but significant differences among Mexican Mestizos from West, Center, and Northeast regions (Fst = 0.01558; p = 0.0000), similar to the observed among three main ethnic groups from USA (Fst = 0.02048; p = 0.0000). This finding is consistent with the contrary clines of European and Amerindian ancestries described throughout the Mexican territory for Mestizos, the largest population (~90 %) in this country.

Paternity tests in Mexico: Results obtained in 3005 cases.

National and international reports regarding the paternity testing activity scarcely include information from Mexico and other Latin American countries. Therefore, we report different results from the analysis of 3005 paternity cases analyzed during a period of five years in a Mexican paternity testing laboratory. Motherless tests were the most frequent (77.27%), followed by trio cases (20.70%); the remaining 2.04% included different cases of kinship reconstruction. The paternity exclusion rate was 29.58%, higher but into the range reported by the American Association of Blood Banks (average 24.12%). We detected 65 mutations, most of them involving one-step (93.8% and the remaining were two-step mutations (6.2%) thus, we were able to estimate the paternal mutation rate for 17 different STR loci: 0.0018 (95% CI 0.0005-0.0047). Five triallelic patterns and 12 suspected null alleles were detected during this period; however, re-amplification of these samples with a different Human Identification (HID) kit confirmed the homozygous genotypes, which suggests that most of these exclusions actually are one-step mutations. HID kits with ≥20 STRs detected more exclusions, diminishing the rate of inconclusive results with isolated exclusions (<3 loci), and leading to higher paternity indexes (PI). However, the Powerplex 21 kit (20 STRs) and Powerplex Fusion kit (22 STRs) offered similar PI (p = 0.379) and average number of exclusions (PE) (p = 0.339) when a daughter was involved in motherless tests. In brief, besides to report forensic parameters from paternity tests in Mexico, results describe improvements to solve motherless paternity tests using HID kits with ≥20 STRs instead of one including 15 STRs.