Evaluating the Recovery of DNA from Adhesive Tape after Exposure to Heat and Humidity: Assessing the Degradation Index and STR Profile

It is not uncommon for forensic DNA samples to be degraded or of low quantity; these types of samples can pose challenges throughout analysis and an informative STR profile is not guaranteed. DNA analysis is also very expensive and timely; therefore, it is necessary to understand where to sample a piece of evidence to obtain the best quality and quantity of DNA from the substrate, especially in the case of trace DNA samples which may be difficult to detect. It is also necessary to know when to proceed with analysis given the quality of the sample. The aim of this research was to evaluate the effect of adhesive tape on the degradation of DNA when exposed to heat and humidity and to assess the usefulness of the QuantifilerTM Trio degradation index to estimate the level of degradation in an STR profile. DNA was deposited on or between layers of duct tape or electrical tape and incubated in a humidity chamber for up to two weeks. The degradation index and profile slope were determined for each sample to assess whether the type of tape or number of layers had a significant effect on the degradation of the DNA sample. Multiple linear regression was also used to assess the relationship between the degradation index, amplification input, and the profile slope. The type of tape, number of layers of tape, and treatment length were found to have a significant effect on the degradation index of DNA samples, however, the treatment length was the only factor that had a significant effect on the slope of the DNA profile. These results indicate that the type of tape and number of layers may significantly affect the degradation of a DNA sample given a long enough treatment period, however the degradation index alone cannot be used to evaluate the level of degradation in a DNA sample or estimate the slope of a DNA profile; factors such as the quantity of DNA amplified and method of degradation affect the profile slope as well