A Study of DNA Degradation for the Purpose of DNA Testing: Analysis of a Method to Improve DNA Profiling on Degraded DNA Samples

Concentration of higher molecular weight DNA allowed for a useable DNA profile to be obtained from a degraded DNA sample. DNA extraction methods were tested with tissue samples under three environmental conditions. The three tissue samples compared the time frame of in which DNA degradation occurred and the recovery of useable DNA profiles, to determine if the level of improvement was reproducible. Short tandem repeats (STRs) and electrophoresis is used in forensic DNA analysis in order to determine a DNA profile. STRs are highly polymorphic regions with short repeated sequences. The Combined DNA Index System (CODIS) developed by the Federal Bureau of Investigation (FBI) consists of thirteen STR loci (D3S1358, THO1, D21S11, D18S51, D5S818, D13S317, D7S820, D16S539, CSF1PO, vWA, D8S1179, TPOX, and FGA). Multiple allelic variants are possible at each locus, which allow the profile obtained to discriminate between individuals. DNA degradation can prevent an acceptable profile from being obtained. DNA degradation, an increased number of smaller DNA fragments, can be caused by heat, bacterial growth, ultraviolet light, time, and other environmental factors. Known DNA profiles were established for the three tissue samples and the profiles were monitored for DNA degradation. The three tested environmental conditions were open air climate, stagnant water conditions and submerged soil conditions. Sections of the tissue samples underwent DNA processing over defined time periods and the allelic profiles were recorded. Once DNA degradation was observed the samples were removed to prevent further degradation and the higher molecular weight DNA was concentrated and an improved DNA profile was obtained in two of the three samples