Semester

Fall

Date of Graduation

2025

Document Type

Thesis (Campus Access)

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Tina Moroose

Committee Member

Kenneth Ryan

Committee Member

William Allan

Abstract

Sexual assault kits contain evidence commonly analyzed in forensic crime laboratories. These items often consist of a mixture of genetic information; typically, from a primary female contributor and minor male contributor. The traditional method of separating the cellular components to identify the contributors is often time consuming and can be ineffective, especially with high female to male ratios of DNA. The current focus of literature is primarily concerned with improving upon the traditional approach of differential separation using methods that rely on differences in cell morphology such as SpermX™, automation, microscopy-, and affinity-based techniques. Despite the reported improvement these techniques have on separation efficiency, they tend to rely upon specialized equipment, operator skill, and/or require increased hands-on time from analysts. Probabilistic systems have been demonstrated to reliably interpret routine sexual-assault DNA mixture evidence that often occurs due to the incomplete separation of traditional differential extraction methods. However, no previous research has explored an approach that forgoes a differential separation in lieu of generating a mixed profile to be interpreted by probabilistic genotyping software. In this study, we investigated the efficacy of a non-differential extraction workflow coupled to probabilistic genotyping in comparison to differential separation workflows interpreted with threshold-driven methods. Our results suggest that while the probative value of match information is similar for differentially-separated samples when interpreted with probabilistic or threshold-driven methods, non-differentially extracted samples could not provide probative match information when interpreted with either method. Forensic laboratories are encouraged to consider the potential increase in sexual assault case productivity with the use of probabilistic mixture interpretation by limiting analysts’ hands-on time in the absence of more efficient and effective extraction methods. However, more investigation into workflows that increase the efficiency of sexual assault kit processing without adding to the labor or monetary costs of forensic laboratories is needed.

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