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MaSTR™: an effective probabilistic genotyping tool for interpretation of STR mixtures associated with differentially degraded DNA

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Abstract

The recently developed probabilistic genotyping software package MaSTR™ (SoftGenetics LLC) was used to develop statistical weight estimates for a variety of two-person STR mixture profiles with differentially degraded sources of DNA. A total of 864 analyses, on 144 two-person profiles, were performed. Mixture ratios ranged from 1:1 to 1:10, including pristine sources of DNA and various combinations of artificially degraded DNA (average size fragments of 150 or 250 bps). Quantities of DNA template were varied (0.1 to 0.5 ngs of total input) and MaSTR™ analysis was performed with eight chains of 10,000 or 40,000 iterations, with or without a conditioning profile to generate likelihood ratio (LR) values. Overall, the software performed as expected. The resulting log(LR) values for pristine mixture profiles were typically greater than 1030. Lower-quality mixture data associated with sources of DNA at ~ 0.05 ngs for each contributor resulted in peak imbalance and allelic dropout which reduced the weight in support of a contributor. This was exacerbated by higher levels of degradation, with some instances resulting in log(LR) values in support of an exclusion. These studies provide additional support for the use of probabilistic genotyping software solutions in forensic investigations, addressing concerns raised by the President’s Council of Advisors on Science and Technology (PCAST).

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Data availability

Data files associated with this study cannot be made available as consent to do so was not obtained.

Code availability

The code for MaSTR™ is proprietary.

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Acknowledgements

The authors wish to thank John Fosnacht, Teresa Snyder-Leiby, Dan Erb, and Sarah Copeland from SoftGenetics LLC for their support with software development and generating reports of MaSTR™ analyses. The authors also wish to thank four anonymous donors for the samples associated with this study.

Funding

Financial support provided by the Eberly College of Science, Department of Biochemistry & Molecular Biology, Forensic Science Program at Penn State University.

Author information

Authors and Affiliations

  1. Forensic Science Program, Department of Biochemistry & Molecular Biology, 339 Whitmore Laboratory, The Pennsylvania State University, University Park, PA, 16,802, USA

    Mitchell M. Holland & Jennifer A. McElhoe

  2. Department of Population Health and Pathobiology, North Carolina State University, 1060 William Moore Drive, Raleigh, NC, 27,607, USA

    Teresa M. Tiedge

  3. Texas Department of Public Safety, Austin Crime Laboratory, 5800 Guadalupe Street, Bldg U, Austin, TX, 78,752, USA

    Abigail J. Bender

  4. Armed Forces Medical Examiner System (AFMES), Dover Air Force Base, Dover, DE , 19,902, USA

    Sidney A. Gaston-Sanchez

  5. SNA International, Contractor Supporting the AFMES, Alexandria, VA, 22,314, USA

    Sidney A. Gaston-Sanchez

Authors
  1. Mitchell M. Holland
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  2. Teresa M. Tiedge
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  3. Abigail J. Bender
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  4. Sidney A. Gaston-Sanchez
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  5. Jennifer A. McElhoe
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Contributions

MMH: experimental design, data analysis, wrote the manuscript; TMT, AJB, and SAG-S: experimental design, laboratory and data analysis, review of the manuscript; JAM: statistical analysis, development of figures, review of the manuscript.

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Correspondence to Mitchell M. Holland.

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Samples were collected with consent according to an Institutional Biosafety Committee approved protocol #IBC-48221.

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Conflict of interest

MMH serves as the Acting Laboratory Director of Mitotyping Technologies, a SoftGenetics company, LLC. MMH receives no monetary compensation for his role as Laboratory Director and has no financial interests in SoftGenetics or Mitotyping Technologies.

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Holland, M.M., Tiedge, T.M., Bender, A.J. et al. MaSTR™: an effective probabilistic genotyping tool for interpretation of STR mixtures associated with differentially degraded DNA. Int J Legal Med 136, 433–446 (2022). https://doi.org/10.1007/s00414-021-02771-0

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  • DOI: https://doi.org/10.1007/s00414-021-02771-0

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