Interpreting DNA profiles manually can potentially call into question subjectivity between analysts who may interpret specific results differently. There are multiple features of a DNA profile that can complicate interpretation, which include allelic dropout and drop-in, allele sharing, and polymerase chain reaction (PCR) artifacts, which can all confound manual interpretation of DNA profiles. Difficulties in interpretation of DNA profile evidence can also be caused by degradation of the DNA itself, which can be caused by various environmental factors. Over the last 15 years, developments in DNA profile interpretation using probabilistic genotyping software (PGS) have been made in order to assist in the complicated task of interpreting and deconvoluting a challenging mixture. Among these PGSs is DNA-View® Mixture Solution™, a continuous-model program that is based on stochastic modeling.
In this research, Mixture Solution was used to provide statistical analyses on DNA mixtures that were subject to various levels of degradation, through the assignment of a likelihood ratio (LR) to the mixture profile. The LR would either support the hypothesis that the person of interest (POI) contributed to the mixture, or support the contrary hypothesis, that the POI was not one of the contributors. Mixtures were prepared at four different contributor ratios with varying combinations of three levels of degradation: no degradation, partial degradation, and full degradation, using controlled heating to systematically degrade the DNA template prior to amplification. Using two hypothesis tests, Mixture Solution was used to compute LRs for each of the mixtures with a variety of defined POIs.
Results showed that Mixture Solution successfully generated appropriate LRs for all 20 mixtures in this research, with no Type I errors that falsely excluded a known contributor from a mixture via an LR less than one. Even with the greatest level of degradation and at the most disproportionate ratio of contributors, Mixture Solution was able to assign an LR to each contributor that confirmed their presence in the mixture. When the DNA of a POI was subjected to degradation, decreases in the LR values were observed when compared to the values computed for undegraded DNA from the same POI. However, in all mixtures, Mixture Solution was able to assign an LR with “moderate support” or higher to each of the POIs in both tests, regardless of the level of degradation.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/48190 |
| Date | 24 February 2024 |
| Creators | Filipe, Cameron Alexandre |
| Contributors | Cotton, Robin W. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0171 seconds