Forensic applications of associating human scalp hair morphology and pigmentation analysis at the microscopic and molecular level

Abstract

Criminal investigation and the science behind evidence analysis is an ever- growing niche, and forensic DNA phenotyping (FDP) is no exception. For years the only information given to authorities regarding DNA found at a crime scene was STR analysis and matching to a comparative DNA sample from a known source. However, what happens when there is no suspect to compare DNA profiles, or the case involves a missing person where the only available piece of evidence is a biological sample found at the scene? Before FDP, not much could be done with the DNA sample and the investigation would be stalled. Now it is becoming possible to statistically predict an individual’s visual characteristics using FDP. Currently, with the use of Irisplex, HIrisplex, and HIrisplex-S, statistical analyses and predictions can be done for categorical eye, hair, and skin color by looking at specific genes and their associative SNPs, such as HERC2 and OCA2. The more that is understood about trait-determining genes and their functional significance with regards to our physical traits, the more phenotypes can be added to these prediction tools. In an effort to discover additional genes associated with human phenotypes, this study looked at thirty-two pigmentation-associated candidate genes, and eleven hair structure and morphology associated genes in owl monkey pelage samples. Although the samples were not of human origin, it is important to point out the high conservation between humans and their non-human primate relatives. The owl monkeys used in this study were helpful for tracking expression levels of genes controlling differentpigmentation and hair structure types, because each monkey had intra-individual variation in thickness and in coat color which allowed the generation of potential candidate genes for human investigation. Of the 43 total candidate genes analyzed, 36 had successful amplification, and 28 showed a significant difference in expression when comparing the different samples. The second part of this study was to compare quantitative characteristics of human hair in physical samples and two-dimensional (2D) photos. A test set of 45 individuals had 3-5 hairs from the vertex of their head plucked and analyzed, and a 2D photograph was taken of their scalp hair. The idea was to be able to make quantitative phenotypes in hair (such as hair width, amount of curl) from 2D imagery, when physical samples are not available for analysis. This is due to the fact that the majority of genotype-phenotype databases consist solely of photographic imagery, and seldom have hairs that can be microscopically prepared for analysis. Defining measurable phenotypes from 2D photos that strongly correlate with their physical counterparts allow for the generation of a more accurate phenotype for future genome wide association studies (GWAS) within and outside this laboratory that study hair thickness and hair curl. Three different quantitative phenotypes were compared between the microscopic and 2D photo- analysis.