Research Article| Volume 16, P98-104, May 2015

The effect of wild card designations and rare alleles in forensic DNA database searches

Published:December 15, 2014DOI:


      • Extensions of previous work on DNA database matching probabilities.
      • Relaxation of exact matching to include wild cards.
      • Incorporates the concepts of rare alleles in DNA database matching.
      • All methods are implemented in open source software.
      • Numerical examples demonstrate the effect of wild cards and rare alleles.


      Forensic DNA databases are powerful tools used for the identification of persons of interest in criminal investigations. Typically, they consist of two parts: (1) a database containing DNA profiles of known individuals and (2) a database of DNA profiles associated with crime scenes. The risk of adventitious or chance matches between crimes and innocent people increases as the number of profiles within a database grows and more data is shared between various forensic DNA databases, e.g. from different jurisdictions.
      The DNA profiles obtained from crime scenes are often partial because crime samples may be compromised in quantity or quality. When an individual's profile cannot be resolved from a DNA mixture, ambiguity is introduced. A wild card, F, may be used in place of an allele that has dropped out or when an ambiguous profile is resolved from a DNA mixture.
      Variant alleles that do not correspond to any marker in the allelic ladder or appear above or below the extent of the allelic ladder range are assigned the allele designation R for rare allele. R alleles are position specific with respect to the observed/unambiguous allele. The F and R designations are made when the exact genotype has not been determined. The F and R designation are treated as wild cards for searching, which results in increased chance of adventitious matches. We investigated the probability of adventitious matches given these two types of wild cards.


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        • Butler J.M.
        Advanced Topics in Forensic DNA Typing: Methodology.
        Elsevier, San Diego, CA, USA2012
        • Williams R.
        • Johnson P.
        • Martin P.
        Genetic Information and Crime Investigation, Technical Report.
        School of Applied Social Sciences, University of Durham, 2004 (ISBN: 0 903 593 19 X)
        • Walsh S.J.
        • Moss D.S.
        • Kleim C.
        • Vintiner G.M.
        The collation of forensic DNA case data into a multi-dimentional intelligence database.
        Sci. Justice. 2002; 42: 205-214
        • Walsh S.J.
        • Moss D.S.
        Forensic DNA databasing – solving crime in New Zealand.
        Australas. Sci. 2001; 22: 34-36
      1. S.J. Walsh, C. Roux, A. Ross, O. Ribaux, J.S. Buckleton, editors. Examaining the role and impact of forensic DNA profiling on key areas of the criminal justice system, in: Presented at the 16th Australian and New Zealand Forensic Science Society International Symposium for the Forensic Sciences; 2002 12–17 May 2002; Canberra, Australia.

        • Weir B.S.
        Matching and partially matching DNA profiles.
        J. Forensic Sci. 2004; 49: 1009-1014
        • Weir B.S.
        The rarity of DNA profiles.
        Ann. Appl. Stat. 2007; 1: 358-370
        • Tvedebrink T.
        • Curran J.M.
        • Eriksen P.S.
        • Mogensen H.S.
        • Morling N.
        Analysis of matches and partial-matches in a Danish STR data set.
        Forensic Sci. Int. Genet. 2012; 6: 387-392
        • Tvedebrink T.
        • Curran J.
        DNAtools: Statistical Functions for Analysing Forensic DNA Databases. R Package Version 0.
        2014: 1-18 (available at CRAN: