The efficacy of DNA mixture to mixture matching

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  We investigate a method to identify a common contributor in two mixed DNA profiles  The discrimination power is limited by the smallest DNA contribution to the profiles  We show good ability to find pairs of profiles with a common contributor  This tool gives the ability to provide intelligence information

A Review of Probabilistic Genotyping Systems: EuroForMix, DNAStatistX and STRmix™

“…This was later extended to include forward stutter (with modelling of forward stutter described in [157,158]), and then generalised so that any number of stutters (and with any size-based relationship to the parent peak), applied to any combination of specific loci, could be added by users with the mathematical framework automatically extending to incorporate them (generalised stutter modelling is described in [155]). The height of coincident peaks (either from multiple allele donations, or allele and stutter) are added [159,160] to produce the final expected peak heights.…”

“…Two mixtures can be compared using DBLR in order to determine whether there is support for a common DNA donor, using the method described by Slooten [20]. Studies into this feature have found a high efficacy for identifying common donors [159]. The process has been shown to have use as a Quality Assurance tool to identify potential sample to sample contamination events [25].…”

“…Reference Ability of STRmix™ to deconvolute profiles and assign LRs that comport to manual interpretation and human expectation [15] Ability of STRmix™ to discriminate between donors and non-donors in database searches [190] Behaviour of STRmix™ to assign LRs when dealing with multiple replicates, different number of contributors, and assumed contributors [163] Sensitivity of LR produced by STRmix™ to different factors of uncertainty such as theta, relatedness of alternate DNA source and length of MCMC analysis [171] Tests to be performed when validating probabilistic genotyping, using STRmix™ as an example [112] Ability of individuals from different laboratories to standardise evaluations when using STRmix™ [33,53] Ability of STRmix™ to reliably use peak height information in very low intensity profiles [56,132,210] Ability of STRmix™ to discriminate between donors and non-donors in large-scale Hd true tests, or using importance sampling [59,60,190,200,21 2,213] Sensitivity of STRmix™ model parameters to laboratory factors [196,198] Ability of STRmix™ to utilise information from profiles produced under different laboratory conditions within a single analysis [155] Effect of mixture complexity, allele sharing and contributor proportions on the ability STRmix™ to distinguish contributors from non-contributors [54] The ability of STRmix™ to identify common DNA donors in mixed samples [25,159] The sensitivity of LRs produced in STRmix™ to the choice of the number of contributors [71,72,97] Ability to use STRmix™ to resolve major components of mixtures [72] Testing the assumption of additivity of peak heights in STRmix™ models [159,160] Performance of the degradation model within STRmix™ [214] The effect of relatedness of contributors to the STRmix™ analysis [203,215] Testing the calibration of LRs produced in STRmix™ [58] Validation overviews of STRmix™ [205,216] Comparison of STRmix™ ...…”

The importance of considering common sources of unknown DNA when evaluating findings given activity level propositions

“…A mixture-to-mixture comparison was carried out (as per the method in [12,13]) and an LR calculated considering the propositions:…”

“…The probability associated with matching background DNA profile is typically set quite low, due to the discrimination power of DNA profiling systems. The value can be assigned based on a match probability if the unknowns are able to be interpreted, or could be based on mixture to mixture comparisons [12,13] if the unknowns are not resolvable. When common unknown donors are found to be present, the evaluation will show that the findings provide strong support for the presence of the alternate offender, as the probability of transfer, persistence and recovery of the DNA of that donor is much higher than matching profiles from different sources present as background.…”