Abstract
BackgroundRecently, the Combined DNA Index System (CODIS) Core Loci Working Group established by the US Federal Bureau of Investigation (FBI) reviewed and recommended changes to the CODIS core loci. The Working Group identified 20 short tandem repeat (STR) loci (composed of the original CODIS core set loci (minus TPOX), four European recommended loci, PentaE, and DYS391) plus the Amelogenin marker as the new core set. Before selecting and finalizing the core loci, some evaluations are needed to provide guidance for the best options of core selection.MethodThe performance of current and newly proposed CODIS core loci sets were evaluated with simplified analyses for adventitious hit rates in reasonably large datasets under single-source profile comparisons, mixture comparisons and kinship searches, and for international data sharing. Informativeness (for example, match probability, average kinship index (AKI)) and mutation rates of each locus were some of the criteria to consider for loci selection. However, the primary factor was performance with challenged forensic samples.ResultsThe current battery of loci provided in already validated commercial kits meet the needs for single-source profile comparisons and international data sharing, even with relatively large databases. However, the 13 CODIS core loci are not sufficiently powerful for kinship analyses and searching potential contributors of mixtures in larger databases; 19 or more autosomal STR loci perform better. Y-chromosome STR (Y-STR) loci are very useful to trace paternal lineage, deconvolve female and male mixtures, and resolve inconsistencies with Amelogenin typing. The DYS391 locus is of little theoretical or practical use. Combining five or six Y-chromosome STR loci with existing autosomal STR loci can produce better performance than the same number of autosomal loci for kinship analysis and still yield a sufficiently low match probability for single-source profile comparisons.ConclusionA more comprehensive study should be performed to provide the necessary information to decision makers and stakeholders about the construction of a new set of core loci for CODIS. Finally, selection of loci should be driven by the concept that the needs of casework should be supported by the processes of CODIS (or for that matter any forensic DNA database).
Highlights
The Combined DNA Index System (CODIS) Core Loci Working Group established by the US Federal Bureau of Investigation (FBI) reviewed and recommended changes to the CODIS core loci
A more comprehensive study should be performed to provide the necessary information to decision makers and stakeholders about the construction of a new set of core loci for CODIS
Selection of loci should be driven by the concept that the needs of casework should be supported by the processes of CODIS
Summary
The Combined DNA Index System (CODIS) Core Loci Working Group established by the US Federal Bureau of Investigation (FBI) reviewed and recommended changes to the CODIS core loci. The rapid growth of the database presents the following new challenges for CODIS, as for other DNA criminal databases: 1) to address the potential of increased adventitious hits; 2) to be able to increase power for current and new applications, such as missing-persons identification and familial searching; and 3) to enable international data exchange. The latter may be of more limited value, for example between the US and Europe or the US and
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