VOLUME 10 NUMBER 1 (January to June 2017)


Philipp. Sci. Lett. 2017 10 (1) 14-21
available online: March 14, 2017

*Corresponding author
Email Address: madeungria@up.edu.ph
Received: 04 November 2015
Revised: 17 August 2016
Accepted: 17 October 2016


Non-differential DNA extraction of post-coital samples submitted as evidence for investigating sexual assault cases in the Philippines

Jae Joseph Russell B. Rodriguez1,2, Gayvelline C. Calacal1, Rita P. Laude2, and Maria Corazon A. De Ungria*1

¹DNA Analysis Laboratory, Natural Sciences Research Institute, University of the
 Philippines Diliman, Quezon City, Philippines, 1101
²Genetics and Molecular Biology Division, Institute of Biological Sciences, University
 of the Philippines Los Baños, Laguna, Philippines, 4031

The number of reported sexual assault cases continues to rise yearly in the Philippines. One major step towards addressing this problem is to use DNA test results in rapidly and accurately identifying assailants. The common practice among forensic laboratories overseas is to perform differential DNA extraction to isolate sperm fraction. For this study, we employed non-differential methods to maximize DNA recovery. We evaluated two non- differential DNA extraction procedures namely a phenol- chloroform-isoamyl alcohol (PCI) method and a silica-based method for handling post-coital samples. The procedures were assessed based on total human DNA yield, quality of DNA extracted from single-source semen samples, and the proportion of male component from post-coital vaginal swabs and stains. Higher DNA yields but lower DNA quality resulted from the PCI method. The silica-based method using QIAamp DNA Micro kit produced better quality DNA, resulted in higher male proportion for male-female samples, was faster and less tedious, minimized exposure to hazardous chemicals, and generated less waste. In the Philippines, where biological samples may be compromised due to the tropical climate favoring enzyme- catalyzed degradation of DNA, as well as delays in a victim reporting the incident, we recommend a non-differential silica- based method to maximize recovery of good quality DNA. This should be followed by statistical interpretation using a continuous model to objectively evaluate results that contain the DNA profiles of victim and assailant.

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