Shannon's equivocation for forensic Y-STR marker selection.

Short tandem repeat (STR) markers are widely and continuously used in forensic applications. However, past research has demonstrated substantial allelic association between STR markers on both autosomes and the X chromosome, leading to partially redundant information that these markers can provide. Here, we quantify the allelic association between Y-chromosomal STR markers that are part of established forensic panels, separately for three different continental groups. We further propose a sequential marker selection procedure that is based on Shannon's equivocation and that accounts for allelic association between STR markers, leading to a maximal gain in independent information. In application to three real-world data sets, we demonstrate the procedure's superior performance when compared to single-locus diversity selection strategies, resulting in the optimal marker set for a given data set in the majority of marker subsets. Noting the inferior performance of the established Y-STR marker panels in a retrospective investigation, we suggest that future forensic marker selection should be guided, besides by other technical selection criteria, by an equivocation-based approach to obtain maximally discriminatory marker sets at minimal cost.