Forensic Genomics

The study to be presented utilized Nile Red dye to visualize hand-touched areas on white cotton while evaluating three DNA collection methods: traditional cutting, combination cutting, and M-Vac^® wet vacuum. Nile Red is a fluorescent dye known to bind to lipids that are likely deposited on substrates during the hand-touch process. Nile Red showed observable fluorescence in 50 of 60 test samples (examination of photographs using digital tools did indicate fluorescence in all 60 samples), clearly locating areas where biological material from human contact was deposited, maximizing the likelihood of obtaining touch DNA from these areas. The M-Vac wet vacuum and combination cutting methods had the highest percentage profiles obtained in the study. Sixteen of 20 samples collected with the combination cutting method and 15 for the M-Vac method resulted in full profiles compared with only 4 samples with the traditional cutting method. The M-Vac method produced the most nondonor alleles (94 alleles in 9 samples) followed by the combination method (12 alleles in 6 samples) and the traditional (9 alleles in 4 samples). Statistical analysis indicates that the M-Vac and the combination methods were not statistically different in DNA concentration, however, the DNA concentrations for both methods were statistically higher than the DNA concentrations obtained by the traditional method. This study shows that utilizing Nile Red as a detection method for areas containing trace DNA in conjunction with improved DNA collection methods is viable for DNA genotyping of trace DNA on cotton fabric. Crime laboratories can implement the combination sample collection method in lieu of traditional cutting methods without expansive changes in protocols or a large increase in laboratory expenditures.

Pigmentation genetics has become an important pillar in the field of forensic genomics for its application in DNA-based prediction of externally visible characteristics (EVCs). EVCs such as hair color, eye color, and skin color are complex traits that are influenced by several loci. When traditional short tandem repeat DNA profiling does not reveal any matches, pigmentation-associated loci can be informative of an individual's EVCs through a process known as forensic DNA phenotyping (FDP). Current FDP panels contain a combined set of over 40 polymorphisms that have been identified as being significantly associated with skin, hair, and eye color. A comprehensive understanding of the genetics underlying pigmentation traits is required to improve the precision and accuracy of FDP estimations. Presented herein is a summary of methods and tools for conducting a genome-wide association study (GWAS) to identify forensically relevant, phenotypically informative single nucleotide polymorphisms. The pipeline described focuses on post-genotyping (i.e., in silico) analyses, with emphasis on association analyses, post-association analyses, and first-pass functional annotation. Using eye color as an example, we demonstrate how the pipeline uses GWAS data to draw preliminary conclusions regarding the location and function of pigmentation-associated variants. The experiment specifically investigates eye color associated variants in individuals with a blue eye color background (rs12913832:GG genotype) in a Canadian dataset. While methodologies and tools available for GWAS and post-GWAS processing continue to evolve and advance, the presented approaches have been applied successfully in numerous association analyses among hundreds of thousands of individuals in a wide range of disciplines. As such, they may offer a road map for future genomics investigations of pigmentation traits as well as other EVCs, ultimately serving to improve statistical predictions of phenotypes in forensic settings.