The interpretation of mixed DNA profiles from a mother, father, and child trio

•Mixtures of a mother, father, child trio are examined using the software STRmix™.•Parent/child allele sharing often results in artificially high or low LRs.•User-informed mixture proportions and an assumed donor parent assists interpretation.•The distribution of LRs for true and false donors is reported. We report the interpretation of three-person mixed DNA profiles constructed from DNA from one mother, father, and child trio using the probabilistic genotyping software STRmix™. A total of 40 mixtures were examined, with varying total template and mixture proportions of the three contributors. In addition, mixtures were artificially degraded at four different rates to test the effects of degradation on the interpretation of mother, father and child trios. A total of 560 STRmix™ analyses were undertaken, examining four different interpretation strategies. Reasonable results were only achieved by conditioning on one parent as an assumed donor and applying a user-informed prior to the mixture proportion of both parents. For each of the 40 amplified mixtures, 10,000 non-donors were compared, conditioning on one parent and applying a user-informed prior to the mixture proportion of both parents. This leads to 800,000 non-donor tests.