Mutation Rate Analysis of 26 Rapidly Mutating Y-STRs in a Tanzanian Male Population

Y-chromosome short tandem repeats (Y-STRs) are widely used in forensic investigations, including sexual assault cases, paternity testing, and disaster victim identification. Despite their usefulness, conventional Y-STRs with low mutation have limitations in distinguishing males within the same paternal lineages. The development of Rapid Mutating Y-Chromosome Short Tandem Repeats with a mutation rate of 10 -2 has enhanced the capacity of differentiating related males. This study aimed to characterize the mutation rate and pattern of 26 Rapidly Mutating Y-Chromosome Short Tandem Repeat (RM Y-STR) loci in Tanzania where population-specific data are lacking for local casework. 138 DNA confirmed unrelated father-son pairs from consented individuals in Dar es Salaam were analyzed. Genomic DNA was extracted using the Chelex 100 method, amplified with the Microreader™ 26 RM-Yplex Amplification Kit, and analyzed by capillary electrophoresis. Mutation events were identified by comparing allele profiles between father and son across all loci. A total of 34 mutations were observed, with the most occurring at a single locus following a stepwise mutation model with a 59% gain and a 41% loss of alleles. DYF399S1 exhibited the highest locus-specific mutation rate (6.5 × 10 -2 ; 95% CI: 3.0 × 10 -2 –1.22 × 10⁻¹), while the overall mutation rate across loci was 1.0 × 10 -2 (95% CI: 6.0 × 10 -3 to 1.3 × 10 -2 ), consistent with global estimates. These results establish RM Y-STRs as a powerful forensic tool for discriminating paternally related males in Tanzania, filling a critical data gap for local casework.