Research

Developing criteria and data to determine best options for expanding the core CODIS loci

Jianye Ge, Arthur Eisenberg and Bruce Budowle

For all author emails, please log on.

Investigative Genetics 2012, 3:1 doi:10.1186/2041-2223-3-1

Published: 6 January 2012

Abstract (provisional)

Background

Recently, the CODIS Core Loci Working Group established by the FBI reviewed and recommended changes for the CODIS core loci. The Working Group identified 20 STR loci comprised of the original CODIS core set loci (minus TPOX), four European recommended loci, Penta E, and DYS391 plus the Amelogenin marker as the new core set. Before selecting and finalizing the core loci some evaluations are in order which could provide guidance for best options of core selection.

Method

The performance of current and newly proposed CODIS core loci sets were evaluated with simplified analyses for adventitious hit rates in reasonably large data sets under single source profile comparisons, mixture comparisons, kinship searches, and for international data sharing. Informativeness (e.g., Match Probability, Average Kinship Index) and mutation rates of each locus are some criteria to consider for loci selection. However, a primary factor should be performance with challenged forensic samples.

Results

The 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 do perform better. Y chromosome STR loci are very useful to trace paternal lineage, deconvolve female and male mixtures, and resolve inconsistencies with Amelogenin typing. The selection by the CODIS Working Group of the DYS391 locus makes little sense theoretically or practically. Combining five or six Y-STR loci with existing autosomal STR loci can have 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.

Conclusion

A more comprehensive study should be sought to provide necessary information to decision makers and stakeholders about constructing a new set of core loci for CODIS. Finally, as food for thought, selection of loci should be driven by the concept that the needs of casework should be supported by CODIS (or for that matter any forensic DNA database).