Date of Submission

5-2026

Document Type

Thesis

Degree Name

Master of Science in Forensic Science

Department

Criminal Justice

Advisor

Heather Miller Coyle, Ph.D.

Committee Member

David San Pietro, Ph.D.

Committee Member

Erik Hall, MSFS

Keywords

IrisPlex Single Nucleotide Polymorphisms (SNPs), Hair, Exogen Phase, Forensic Phenotypic Prediction, HERC2/OCA2 Genes, Forensic Investigative Genetic Genealogy (FIGG)

MeSH

Polymorphism, Single Nucleotide, Genotype, Eye Color, Phenotype, HERC2 Protein, Human, OCA2 Protein, Human

LCSH

Single nucleotide polymorphisms, Hair, Color of eyes, Forensic genetics, Genealogy

Abstract

Forensic science increasingly relies on DNA evidence; however, traditional short tandem repeat (STR) analysis has limitations when applied to degraded samples, such as hairs in the exogen phase. This preliminary study investigates the recovery and prediction accuracy of IrisPlex single nucleotide polymorphisms (SNPs) from exogen-stage human hair samples to determine how factors like hair color and shaft location influence SNP recovery and phenotypic eye color predictions. The analysis focuses on the IrisPlex SNPs rs12913832 (HERC2 gene) and rs1800407 (OCA2 gene), which are strongly associated with eye color variation. Hair samples were collected from twelve donors aged 18-26, representing natural brown, blonde, and black hair, along with buccal swabs serving as reference samples. Nuclear DNA extraction, quantification, and SNP genotyping using custom TaqMan assays were performed. Hair shafts were segmented into proximal (root), midshaft, and distal (end) regions to evaluate SNP recovery across the entire length of the hair. Predicted eye color probabilities were generated from SNP profiles and compared to documented phenotypes to assess prediction accuracy. SNP recovery rates for both HERC2 and OCA2 were calculated for the samples. Chi­ square tests of independence were performed to evaluate the statistical significance of hair color and shaft location on SNP recovery rates and genotype concordance between the buccal swab references and hair-derived samples. This study aims to improve understanding of the factors that may affect DNA yield and SNP-based prediction accuracy in degraded hair samples. The findings have potential applications in forensic investigations where hair is the only available biological evidence, including cases involving violent crime and missing people. This work contributes to the advancement of forensic phenotypic profiling and supports the broader application of Forensic Investigative Genetic Genealogy (FIGG) via SNP analysis, though much more future work can be completed to add onto these findings.

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