Highlights
- •Mixtures of two or three relatives are constructed.
- •These are compared with further relatives and unrelated persons.
- •Some triads deconvolute incorrectly.
- •The rate of adventitious support is generally higher for relatives.
- •Conditioning and informed mixture proportion priors are highly useful.
Abstract
The interpretation of mixtures containing related individuals can be difficult due
to allele sharing between the contributors. Challenges include the assignment of the
number of contributors (NoC) to the mixture with the under assignment of NoC resulting
in false exclusions of true donors. Non-donating relatives of the true contributors
to mixtures of close relatives can result in likelihood ratios supporting their adventitious
inclusion within the mixture. We examine the effect of non-donor likelihood ratios
on mixtures of first order relatives. Mixtures of full siblings and parent-child were
created by mixing the DNA from known family members in vitro, or by in silico simulation.
Mixtures were interpreted using the probabilistic genotyping software STRmix™ and
likelihood ratios were assigned for the true donors and non-donors who were either
further relatives of the true donors or unrelated to the true donors. The two donor
balanced mixtures deconvoluted straightforwardly when analysed as NoC = 2 giving approximately
the experimental design 1:1 ratio. When analysed as NoC = 3 a very large number of
non-donor genotypes produced LRs close to 1 including many instances of adventitious support. The in vitro three
donor balanced mixtures proved difficult to assign as NoC = 3 by a blind examination
of the profile. It is likely that many of these would be misassigned as NoC = 2. The
analysis of the in vitro and in silico mixtures assuming NoC = 3 with no use of a
conditioning profile or with the use of a conditioning profile but without informed
priors on the mixture proportions (Mx priors) was ineffective. If the profile can
be assigned as NoC = 3 then assignment of the Mx priors is straightforward. This analysis
gave no false exclusions. Adventitious support did happen for relatives with high
allele sharing. Adventitious support was not observed for any unrelated non-donors.
The analysis of the three-person mixtures as NoC = 2 produced many false exclusions
and fewer instances of adventitious support. The three donor unbalanced mixtures could
all be assigned as NoC= 3. Analysis without Mx priors produced an alternate genotype
explanation.
Keywords
To read this article in full you will need to make a payment
Purchase one-time access:
Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online accessOne-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:
Subscribe to Forensic Science International: GeneticsAlready a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
References
- Probabilistic genotyping software: an overview.Forensic Sci. Int. Genet. 2019; 38: 219-224
- Evaluating DNA profiles in a case where the defence is "it was my Brother".J. Forensic Sci. Soc. 1992; 32: 5-14
- Weight-of-Evidence for Forensic DNA Profiles.John Wiley and Sons, Chichester2005
- Relatedness and DNA: are we taking it seriously enough?.Forensic Sci. Int. 2005; 152: 115-119
President’s Council of Advisors on Science and Technology, An Addendum to the PCAST Report on Forensic Science in Criminal Courts, 2016. 〈https://obamawhitehouse.archives.gov/sites/default/files/microsites/ostp/PCAST/pcast_forensics_addendum_finalv2.pdf〉. (Accessed 8 February 2022).
President’s Council of Advisors on Science and Technology, Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods, 2016. 〈https://obamawhitehouse.archives.gov/sites/default/files/microsites/ostp/PCAST/pcast_forensic_science_report_final.pdf〉. (Accessed 14 December 2021).
- Internal validation of STRmix™ - a multi laboratory response to PCAST.Forensic Sci. Int. Genet. 2018; 34: 11-24
Butler JM, Iyer H., Press R., Taylor MK, Vallone PM, Willis S. , NISTIR 8351-DRAFT, DNA Mixture Interpretation: a NIST Scientific Foundation Review, 2021. 〈https://nvlpubs.nist.gov/nistpubs/ir/2021/NIST.IR.8351-draft.pdf〉. (Accessed 23 August 2021).
- EuroForMix: An open source software based on a continuous model to evaluate STR DNA profiles from a mixture of contributors with artefacts.Forensic Sci. Int. Genet. 2016; 21: 35-44
- Developmental validation of STRmix™, expert software for the interpretation of forensic DNA profiles.Forensic Sci. Int. Genet. 2016; 23: 226-239
- Validating TrueAllele® DNA mixture interpretation.J. Forensic Sci. 2011; 56: 1430-1447
- The interpretation of single source and mixed DNA profiles.Forensic Sci. Int. Genet. 2013; 7: 516-528
- The interpretation of mixed DNA profiles from a mother, father, and child trio. Forensic Science.Int.: Genet. 2020; 44102175
- Population data on the expanded CODIS core STR loci for eleven populations of significance for forensic DNA analyses in the United States.Forensic Sci. Int. Genet. 2016; 25: 175-181
- Does the use of probabilistic genotyping change the way we should view sub-threshold data?.Aust. J. Forensic Sci. 2017; 49: 78-92
President’s Council of Advisors on Science and Technology, Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods, 2016. 〈https://obamawhitehouse.archives.gov/sites/default/files/microsites/ostp/PCAST/pcast_forensic_science_report_final.pdf〉. (Accessed 22 April 2017).
- Developing allelic and stutter peak height models for a continuous method of DNA interpretation.Forensic Sci. Int. Genet. 2013; 7: 296-304
- Developmental validation of a software implementation of a flexible framework for the assignment of likelihood ratios for forensic investigations.Forensic Sci. Int. Rep. 2021; 4100231
- Testing likelihood ratios produced from complex DNA profiles.Forensic Sci. Int. Genet. 2015; 16: 165-171
- Relaxing the assumption of unrelatedness in the numerator and denominator of likelihood ratios for DNA mixtures.Forensic Sci. Int. Genet. 2021; 51102434
- Evaluating DNA evidence possibly involving multiple (mixed) samples, common donors and related contributors.Forensic Sci. Int. Genet. 2021; 54102532
- Distinguishing between donors and their relatives in complex DNA mixtures with binary models.Forensic Sci. Int. Genet. 2016; 21: 95-109
- Familial searching on DNA mixtures with dropout.Forensic Sci. Int. Genet. 2016; 22: 128-138
- The analogy between DNA kinship and DNA mixture evaluation, with applications for the interpretation of likelihood ratios produced by possibly imperfect models.Forensic Sci. Int. Genet. 2021; : 52
- Identifying common donors in DNA mixtures, with applications to database searches.Forensic Sci. Int. Genet. 2017; 26: 40-47
- The likelihood ratio as a random variable for linked markers in kinship analysis.Int J. Leg. Med. 2016; 130: 1445-1456
- Comparing multiple POI to DNA mixtures.Forensic Sci. Int. Genet. 2021; 52102481
- DNA commission of the International society for forensic genetics: Assessing the value of forensic biological evidence - guidelines highlighting the importance of propositions: part I: evaluation of DNA profiling comparisons given (sub-) source propositions.Forensic Sci. Int. Genet. 2018; 36: 189-202
- Using the nondonor distribution to improve communication and inform decision making for low LRs from minor contributors in mixed DNA profiles.J. Forensic Sci. 2020; 65: 1072-1084
Article info
Publication history
Published online: March 21, 2022
Accepted:
March 17,
2022
Received in revised form:
February 15,
2022
Received:
November 19,
2021
Identification
Copyright
© 2022 Elsevier B.V. All rights reserved.
