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On the exact distribution of the numbers of alleles in DNA mixtures

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Abstract

When more than one individual contributes biological material to a forensic stain, the resulting DNA type is termed a DNA mixture. DNA mixtures occur frequently in forensic genetic casework, and in recent years, much research has been devoted to this subject. This paper presents a derivation of the exact distribution of the number of alleles for any number of profiles and investigated loci. The per locus number of observed alleles is of interest as it indicates the plausible range on the number of contributors. Hence, by specifying a prior distribution on the number of contributors, the locus distribution may be used to assess the number of contributors. Furthermore, the total number of alleles across all loci is used by some forensic geneticists to estimate the probability that an allele has failed to be detected (allelic drop-out).

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Acknowledgments

The author would like to thank two anonymous reviewers for the helpful comments which improved the paper. Furthermore, the author is grateful for allele frequencies for the SGM Plus loci and crime case data provided by The Section of Forensic Genetics, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark. This paper has benefited from discussions with Poul Svante Eriksen, Aalborg University and Prof. Niels Morling, The Section of Forensic Genetics, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.

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Authors and Affiliations

  1. Department of Mathematical Sciences, Aalborg University, Fredrik Bajers Vej 7G, 9220, Aalborg East, Denmark

    Torben Tvedebrink

  2. Section of Forensic Genetics, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

    Torben Tvedebrink

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  1. Torben Tvedebrink
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Correspondence to Torben Tvedebrink.

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Tvedebrink, T. On the exact distribution of the numbers of alleles in DNA mixtures. Int J Legal Med 128, 427–437 (2014). https://doi.org/10.1007/s00414-013-0951-3

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  • DOI: https://doi.org/10.1007/s00414-013-0951-3

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