Date of Award

Summer 8-26-2020

Document Type

Thesis

Degree Name

Master of Science (MS)

Department/Program

Forensic Science

Language

English

First Advisor

Mechthild Prinz

Second Reader

Lissette Delgado-Cruzata

Third Advisor

David Fisher

Abstract

Effective DNA extraction methods are important for forensic applications. The main goal of this experiment was to determine if a newly developed trypsin based protein/DNA co-extraction method applied to contact traces would yield comparable results to a commercial Proteinase K method (QIAamp DNA Investigator Kit) and a Chelex extraction method with Tween 20 used in forensic laboratories. This was tested on 20 sets of sebaceous fingerprints on glass slides.

The results of this study demonstrate the trypsin co-extraction method yielded the highest amount of DNA. In the first comparison, the mean total DNA yields for the trypsin-co extraction method and QIAamp DNA Investigator were 6.71 ± 10.69 ng and 0.50 ± 0.54 ng respectively. This difference was significant. For the second comparison, the mean total DNA yields for the trypsin-co extraction method and Chelex Tween 20 extraction method were 8.14 ± 13.83 ng and 4.01 ± 3.99 ng. This smaller difference was not significant. The co-extraction method produced more complete STR profiles than the other methods.

The protein fraction was mass spectrometry compatible. Peptide and protein analysis revealed, on average 393.10 ± 248.01 unique peptides and 44.55 ± 26.74 identified proteins. Fifteen proteins were found in almost all fingerprint residue samples with the majority being keratin type I or II proteins. DNA and protein findings were reproducible when compared to results of a second study testing single thumb prints collected from the same volunteers on the same day. Results of this study demonstrate the trypsin co-extraction method is comparable to already established DNA extraction methods.

Available for download on Thursday, August 26, 2021

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