DNA Degradation and Postmortem Interval: Preliminary Observations and Methods

As deoxyribonucleic acid (DNA) research advances, anthropologists are finding more ways to use this technology to their advantage. Establishing postmortem interval (PMI) is a primary goal of forensic anthropology. It is known that DNA degrades, or breaks down, after an organism dies. Although several researchers have studied DNA degradation, few have focused on DNA’s rate of decay in relation to time. In this project, degradation was examined in blood using both a controlled atmosphere and exposure to environmental and substrate effects.
This study was intended to gather information on PMI, using DNA degradation as a measure of time. Based on the current literature and knowledge of the properties of DNA, it was hypothesized that DNA would decay in a time-dependent manner in a controlled atmosphere. In addition, it was hypothesized that DNA exposed to environmental and substrate effects would decay more rapidly than in a controlled environment.
It was found that DNA of all four fragment lengths, ranging from 110 to 782 base pairs (bp), survived for at least eight days in a controlled atmosphere. Samples exposed to environmental and substrate effects exhibited what might have been degradation, but a way to quantitate the amount of DNA present in each sample is needed. One way to achieve this goal is to use fluorescently labeled PCR products and compare the intensities of the PCR product across samples and time.
The efforts put forth in this project have lead to the development of a system that is likely to be useful in the analysis of degraded DNA. It is clear that DNA analysis will continue to be a tool anthropologists should and will use in the continual effort to determine PMI.