Internal Validation of MaSTR™ Probabilistic Genotyping Software for the Interpretation of 2–5 Person Mixed DNA Profiles

Abstract

Mixed human deoxyribonucleic acid (DNA) samples present one of the most challenging pieces of evidence that a forensic analyst can encounter. When multiple contributors, stochastic amplification, and allele drop-out further complicate the mixture profile, interpretation by hand becomes unreliable and statistical analysis problematic. Probabilistic genotyping software has provided a tool to address complex mixture interpretation and provide likelihood ratios for defined sets of propositions. The MaSTR™ software is a fully continuous probabilistic system that considers a wide range of STR profile data to provide likelihood ratios on DNA mixtures. Mixtures with two to five contributors and a range of component ratios and allele peak heights were created to test the validity of MaSTR™ with data similar to real casework. Over 280 different mixed DNA profiles were used to perform more than 2600 analyses using different sets of propositions and numbers of contributors. The results of the analyses demonstrated that MaSTR™ provided accurate and precise statistical data on DNA mixtures with up to five contributors, including minor contributors with stochastic amplification effects. Tests for both Type I and Type II errors were performed. The findings in this study support that MaSTR™ is a robust tool that meets the current standards for probabilistic genotyping.

Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019–2022

“…In the past three years, validation studies have been performed with a number of probabilistic genotyping software (PGS) systems including EuroForMix [ 278 ], DNAStatistX [ 279 , 280 ], TrueAllele [ 281 ], STRmix [ 282 ], Statistefix [ 283 ], Mixture Solution [ 284 ], Kongoh [ 285 ], and MaSTR [ 286 , 287 ]. Developers of EuroForMix, DNAStatistX, and STRmix provided a review of these systems [ 288 ].…”

Separation mixed semen of two individuals using magnetic beads coupled ABH blood group antibody

“…In the statistical analysis of peak height and peak area of the short tandem repeat (STR) typing analysis, factors such as DNA concentration and the proportion of mixed samples can impact the results, making it difficult to eliminate the influence of shadow bands, nonspecific bands, amplification imbalance, and allele imbalance [4,5]. Through the statistical analysis of mixed DNA profiles, it becomes possible to interpret the potential STR genotypes of each individual [5,6]. Additionally, Y-STR profiles can be assessed using a likelihood ratio method [7], although personal identification is not always possible.…”

Decreased accuracy of forensic DNA mixture analysis for groups with lower genetic diversity

“…Estimates of the number of contributors are less reliable for groups with lower genetic diversity 33 . Variation in LRs has been observed across broadly defined groups (all with relatively high genetic diversity) 32,34,35 . These results all suggest variability in the accuracy of mixture analysis across genetic backgrounds.…”