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Taylor D.,Forensic Science South Australia | Bright J.-A.,ESR Ltd | Buckleton J.,ESR Ltd
Forensic Science International: Genetics | Year: 2013

A method for interpreting autosomal mixed DNA profiles based on continuous modelling of peak heights is described. MCMC is applied with a model for allelic and stutter heights to produce a probability for the data given a specified genotype combination. The theory extends to handle any number of contributors and replicates, although practical implementation limits analyses to four contributors. The probability of the peak data given a genotype combination has proven to be a highly intuitive probability that may be assessed subjectively by experienced caseworkers. Whilst caseworkers will not assess the probabilities per se, they can broadly judge genotypes that fit the observed data well, and those that fit relatively less well. These probabilities are used when calculating a subsequent likelihood ratio. The method has been trialled on a number of mixed DNA profiles constructed from known contributors. The results have been assessed against a binary approach and also compared with the subjective judgement of an analyst. © 2013 Elsevier Ireland Ltd. All rights reserved.


Taylor D.,Forensic Science South Australia | Bright J.-A.,ESR Ltd | Buckleton J.,ESR Ltd | Curran J.,University of Auckland
Forensic Science International: Genetics | Year: 2014

A typical assessment of the strength of forensic DNA evidence is based on a population genetic model and estimated allele frequencies determined from a population database. Some experts provide a confidence or credible interval which takes into account the sampling variation inherent in deriving these estimates from only a sample of a total population. This interval is given in conjunction with the statistic of interest, be it a likelihood ratio (LR), match probability, or cumulative probability of inclusion. Bayesian methods of addressing database sampling variation produce a distribution for the statistic from which the bound(s) of the desired interval can be determined. Population database sampling uncertainty represents only one of the sources of uncertainty that affects estimation of the strength of DNA evidence. There are other uncertainties which can potentially have a much larger effect on the statistic such as, those inherent in the value of Fst, the weights given to genotype combinations in a continuous interpretation model, and the composition of the relevant population. In this paper we model the effect of each of these sources of uncertainty on a likelihood ratio (LR) calculation and demonstrate how changes in the distribution of these parameters affect the reported value. In addition, we illustrate the impact the different approaches of accounting for sampling uncertainties has on the LR for a four person mixture.


Bright J.-A.,ESR Ltd | Bright J.-A.,University of Auckland | Taylor D.,Forensic Science South Australia | Curran J.M.,University of Auckland | Buckleton J.S.,ESR Ltd
Forensic Science International: Genetics | Year: 2013

Traditional forensic DNA interpretation methods are restricted as they are unable to deal completely with complex low level or mixed DNA profiles. This type of data has become more prevalent as DNA typing technologies become more sensitive. In addition they do not make full use of the information available in peak heights. Existing methods of interpretation are often described as binary which describes the fact that the probability of the evidence is assigned as 0 or 1 (hence binary) (see for example [1] at 7.3.3). These methods are being replaced by more advanced interpretation methods such as continuous models. In this paper we describe a series of models that can be used to calculate expected values for allele and stutter peak heights, and their ratio SR. This model could inform methods which implement a continuous method for the interpretation of DNA profiling data. © 2013 Elsevier Ireland Ltd.


Buckleton J.S.,ESR Ltd. | Krawczak M.,University of Kiel | Weir B.S.,University of Washington
Forensic Science International: Genetics | Year: 2011

Mitochondrial DNA (mtDNA) and the non-recombining portion of the Y-chromosome are inherited matrilinealy and patrilinealy, respectively, and without recombination. Collectively they are termed 'lineage markers'. Lineage markers may be used in forensic testing of an item, such as a hair from a crime scene, against a hypothesised source, or in relationship testing. An estimate of the evidential weight of a match is usually provided by a count of the occurrence in some database of the mtDNA or Y-STR haplotype under consideration. When the factual statement of a count in the database is applied to a case, issues of relevance of the database and sampling uncertainty may arise. In this paper, we re-examine the issues of sampling uncertainty, the relevance of the database, and the combination of autosomal and lineage marker evidence. We also review the recent developments by C.H. Brenner. © 2010 Elsevier Ireland Ltd. All rights reserved.


Simons J.L.,ESR Ltd | Vintiner S.K.,ESR Ltd
Journal of Forensic Sciences | Year: 2012

Currently, there is no accurate method to differentiate vaginal epithelial cells from buccal epithelial cells in biological samples typically encountered in forensic casework. This study tested the expression of a selection of candidate proteins in buccal and vaginal epithelial cells. We investigated six candidate biomarkers, such as loricrin, vimentin, stratifin, cytokeratin 4, cytokeratin 13, small proline-rich protein 2, and involucrin, using Western blot analysis on whole protein extracts and immunohistochemistry (IHC) on intact cells in an attempt to identify cell-specific markers that would differentiate these cells by microscopy. Involucrin, loricrin, and stratifin showed differential expression during Western blot analysis and were carried through to IHC. Although proteins unique to vaginal epithelial cells and buccal epithelial cells were not identified from among the proteins tested, the increased expression levels of two proteins, loricrin and stratifin in vaginal cells, when compared to buccal cells, do provide encouraging results in the search for epithelial cell-specific markers. © 2012 American Academy of Forensic Sciences.


Buckleton J.,ESR Ltd. | Myers S.,Jan Bashinski DNA Laboratory
Forensic Science International: Genetics | Year: 2014

Walsh et al. [1] outlined a method for adjusting autosomal coancestry values, θA, to take account of the existence of a Y chromosome match, θA|Y. The framework established by Walsh et al. is flexible and allows an investigation of some real world effects such as family structure. It also allows the effect of a Y chromosome match to be placed within the construct of existing casework practice. Most notable is the ability to deal with an assigned value for the autosomal coancestry coefficient and the fact that most casework statistics report a value for unrelated individuals unless case circumstances suggest differently. The values of θA|Y are not much larger than θA and a coherent argument could be made that any adjustment is unnecessary. © 2014 Elsevier Ireland Ltd. All rights reserved.


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