Despite its capabilities to automate and streamline the analysis of single source samples, an Expert System is as yet unable to make the final analysis decision for most forensic casework samples and in particular for those containing mixtures. It may be possible however to harness the automated, rule-based, subject-specific knowledge on which an Expert System is based to enable the software to act as an Expert Assistant to the forensic analyst, simplifying much of the analysis process and empowering the analyst to make key interpretation decisions confidently and consistently.
Given the nature of forensic casework evidence, there is an increased probability that each sample may contain DNA from more than one individual. This fact coupled with the limitations of using PCR to amplify STR markers requires that casework samples are reviewed in more detail by the forensic expert. By using Expert Assistant software, the forensic analyst should be able to assess controls and QC data, easily review and edit profiles and process mixed samples consistently and reproducibly. GeneMapper® ID-X Software was designed specifically to be an Expert Assistant, automating as much of the casework analysis workflow as possible, enabling the analyst to make key interpretation decisions more quickly and confidently.
Of all the stages involved in analysis of casework evidence, interpretation of mixed samples is one of the most difficult and time-consuming. Despite this, many of the steps in this process can be automated based on a series of rules. Once optimized and validated, these rules can guide the analyst to make a more informed decision based on all of the available data. The GeneMapper® ID-X Mixture Analysis tool quickly identifies the number of contributors within a sample in order to direct each sample along the appropriate workflow. Samples containing either 1 or 3 or more contributors can be reviewed by the analyst prior to performing statistical calculations integrated within the Mixture Analysis tool. Samples containing 2 contributors are evaluated based on mixture proportion and peak height ratio thresholds to produce a restricted set of genotype combinations which helps the analyst to identify the individual contributors to the mixture. The individual genotypes can be extracted with or without consideration of a known reference and the results subjected to statistical analysis.
The process of evaluating all possible genotype combinations for a 2-person mixture is probably the most laborious step involved in mixture analysis if performed manually. The Mixture Analysis tool not only rapidly and accurately considers all possible genotype combinations, taking into account all of the available data, but ranks those possibilities so the analyst can easily identify the most likely contributor profiles. Where a known reference is specified, the software indicates where a match occurs and further filters the display options to only those possible genotype combinations where the known is included. The list of possible genotype combinations can also be displayed in the context of the Samples Plot allowing the analyst to have access to the electropherogram data when deciding which of the combinations to include in subsequent statistical analysis.
And finally, the software is able to combine results from replicate amplifications of the same sample (containing either 1 or 2 contributors) with either the same or different AmpFℓSTR® Kits (e.g. Profiler Plus® and COfiler® Kits) to create a merged profile on which statistical calculations can be performed.
The GeneMapper® ID-X Software has been designed specifically to act as an Expert Assistant, supporting the analyst throughout the casework analysis process and enabling the decisions associated with the analysis of casework samples to be made quickly, consistently and with increased confidence.