Evaluation of RMplex system for differentiating father-son pairs using Y-STRs in a Korean population

Y-chromosomal short tandem repeats (Y-STRs) at rapidly mutating (RM) loci have been suggested as tools for differentiating paternally related males. RMplex is a recently developed system that incorporates 26 RM loci and four fast-mutating (FM) loci, targeting 44 male-specific loci. Here, we evaluated the RMplex by estimating Y-STR mutation rates and the overall differentiation rates for 542 Korean father-son pairs, as well as the genetic population values for 409 unrelated males. RMplex performed well, distinguishing 50.7 % of the father-son pairs by at least one mutation, a value 10 times higher than the previously reported differentiation rate achieved using the PowerPlex® Y23 System. Of the 369 mutations, 361 (97.8 %) were single-step mutations, with locus-specific mutation rates varying from 1.8 × 10^-3 to 1.1 × 10^-1 mutations per generation, and an average mutation rate of 2.3 × 10^-2. Gene diversity values ranged from 0.5696 for DYS442 to 0.9970 for DYF1000, and the haplotype discrimination capacity of unrelated males was 100 %. Among the loci studied, DYS712 exhibited the highest mutation rate in this study of the Korean population. Similarly, the mutation rate of this locus is reported to be substantially higher for the Japanese and Chinese populations than for European populations. These findings suggest that DYS712 mutations are relatively frequent in East Asian populations. Although we did not detect significant relationships among the Y-chromosome single nucleotide polymorphism-based haplogroups, allele length was strongly correlated with the mutation rate at DYS712, which is consistent with previous studies. Although the incorporation of multi-copy loci into RMplex contributed significantly to the high mutation rates detected and to its discrimination capacity, this requires careful interpretation, owing to the potential for duplications. Nonetheless, these findings provide evidence regarding the suitability of the RMplex for distinguishing paternally related males in the Korean population.