Differentiation of Hair from Individuals with Similar Hair Color Using Amino Acid Ratios Obtained from GC-MS Analysis

Emma Brownlie

Date of Submission

5-2024

Document Type

Thesis

Degree Name

Master of Science in Forensic Science

Department

Forensic Science

Advisor

Alyssa L. M. Marsico, Ph.D.

Committee Member

Ted Schwartz, M.S.

Committee Member

Nikolas Stasulli, Ph.D.

Keywords

Human Hair, Trace Evidence, Nuclear DNA Analysis, GC-MS Analysis, Amino Acids

MeSH

Hair, Nucleotides, DNA, Gas Chromatography-Mass Spectrometry, Amino Acids

LCSH

Hair--Analysis, Trace evidence, Nucleotide sequence, DNA--Analysis, Amino acids

Abstract

Hair trace evidence is currently analyzed using microscopic hair comparison (MHC) and DNA analysis. Both nuclear and mitochondrial analysis can be done, but only nuclear DNA analysis can individualize samples. Traditional MHC is subjective, and DNA cannot be performed on inadequate samples. Recently, single nucleotide polymorphisms, which result in non-synonymous amino acid changes in the hairs protein sequences, are being explored as a potential alternative method for forensic hair analysis. Genetically variant peptides have been used in proteomic analysis for non-related individuals, but amino acids may provide a less complicated method of analysis. This method has been used for differentiating between plants, bee propolis and humans. In humans, amino acids have been shown to differentiate individuals based on their demographic and geographic characteristics. A study by Yaroshuk evaluated the discriminating power of amino acid ratios in mainly dark-haired individuals using gas chromatography-mass spectrometry (GC-MS). Expanding on this study, this research included alternative hair colors to further evaluate the use of amino acid ratios to differentiate between individuals using GC-MS analysis. This continued research aims to develop a method that can be used to supplement traditional MHC when DNA analysis cannot be conducted.

Samples were collected from 17 individuals. Microscopic hair images were obtained for RGB analysis in order to group individuals by similar hair color. Samples were divided into 4 RGB groupings. The peak areas obtained from GC-MS analysis were used to calculate amino acid ratios for comparison between individuals and, out of 45 possible amino acid ratios, 21 were used for comparison. Of those ratios, 5 were determined to be highly variable between individuals with similar hair color. T-tests showed that the differences in amino acid ratios between the individuals with similar hair color were statistically significant.

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