A mixed DNA profile controversy revisited

Semaan et al. (J Forensic Res, 2020, 11, 453) discuss a mock case “where eight different individuals [P1 through P8] could not be excluded in a mixed DNA analysis. Even though … expert DNA mixture analysis software was used.” Two of these are the true donors. The LRs reported are incorrect due to th...

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Bibliographic Details
Published inJournal of forensic sciences Vol. 67; no. 1; pp. 128 - 135
Main Authors Kalafut, Tim, Pugh, Simone, Gill, Peter, Abbas, Sarah, Semaan, Marie, Mansour, Issam, Curran, James, Bright, Jo‐Anne, Hicks, Tacha, Wivell, Richard, Buckleton, John
Format Journal Article
LanguageEnglish
Published United States Wiley Subscription Services, Inc 01.01.2022
Subjects
Alleles
Conditioning
DNA
DNA Fingerprinting
DNA fingerprints
DNA mixtures
exhaustive propositions
forensic DNA analysis
Forensic Genetics
Humans
Likelihood Functions
LRmix
Male
Microsatellite Repeats
probabilistic genotyping
relatives
Software
STRmix
DNA mixtures
LRmix
STRmix
exhaustive propositions
forensic DNA analysis
relatives
probabilistic genotyping
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Summary:Semaan et al. (J Forensic Res, 2020, 11, 453) discuss a mock case “where eight different individuals [P1 through P8] could not be excluded in a mixed DNA analysis. Even though … expert DNA mixture analysis software was used.” Two of these are the true donors. The LRs reported are incorrect due to the incorrect entry of propositions into LRmix Studio. This forced the software to account for most of the alleles as drop‐in, resulting in LRs 60–70 orders of magnitude larger than expected. P1, P2, P4, P5, and P8 can be manually excluded using peak heights. This has relevance when using LRmix which does not use peak heights. We extend the work using the same two reference genotypes who were the true contributors as Semaan et al. (J Forensic Res, 2020, 11, 453). We simulate three two‐donor mixtures with peak heights using these two genotypes and analyze using STRmix™. For the simulated 1:1 mixture, one of the non‐donors’ LRs supported him being a contributor when no conditioning was used. When considered in combination with any other potential donors (i.e., with conditioning), this non‐donor was correctly eliminated. For the 3:1 mixture, all results correctly supported that the non‐donors were not contributors. The low‐template 4:1 mixture LRs with no conditioning showed support for all eight profiles as donors. However, the results from pair‐wise conditioning showed that only the two ground truth donors had LRs supporting that they were contributors to the mixture. We recommend the use of peak heights and conditioning profiles, as this allows better sensitivity and specificity even when the persons share many alleles.
Bibliography:Funding information
Previous to this submission, the problem described in this paper was presented by three of the authors (Semaan, Abbas, Mansour) in the Journal of Forensic Research (2020); at the 21st Triannual Meeting of the International Association of Forensic Sciences, August 21–25, 2017, in Toronto, Canada; and at the 73rd Annual Scientific Meeting of the American Academy of Forensic Sciences, February 15–19, 2021, held virtually. Semaan, Abbas, and Mansour have agreed to join the rest of the authors in acknowledging the initial presentations were incorrect, and this paper describes a more appropriate solution.
This work was supported in part by grant NIJ 2020‐DQ‐BX‐0022 from the US National Institute of Justice. Points of view in this document are those of the authors and do not necessarily represent the official position or policies of their organizations.
ISSN:0022-1198
1556-4029
DOI:10.1111/1556-4029.14912