Consider an old bone sample that is highly degraded or a heterogenous sample with high female to male DNA content. It is challenging to obtain useful STR marker information from such samples in order to upload to a database and find a match. However, the chances of recovering a quality STR profile are higher when using 6-dye chemistries that offer superior discriminatory power, maximum sensitivity and high tolerance to inhibition.
A recent degradation study was conducted by the University of North Texas Health Science Center, Department of Forensic and Investigative Genetics, US, comprising a set of 15 bone samples, including specimens dating back to the late 19th century. The bone sample extracts were analyzed using the Applied Biosystems™ GlobalFiler™ chemistry as well as a competitive STR chemistry. Overall, samples processed using the GlobalFiler kit showed better allele recovery than results from the competitive chemistry which exhibited more drop-out/allele loss. For the male bone samples, analyzed with an analytical threshold as low as 50 RFU threshold, all male markers were recovered using the GlobalFiler™ kit while results from the competitive chemistry exhibited loss of the rapidly mutating Y-marker positions.
Thus, even within the available set of 6 dye technologies, assessing STR kit performance on real-world samples becomes important when selecting the right chemistry.
Dr. Antonio Alonso, a DNA expert at the National Institute of Toxicology and Forensic Sciences, Madrid (Spain), in a recent interview, stresses the need for forensic laboratories to make that transition to 6-dye chemistries in order to gain workflow efficiency and reduce operating costs. He further highlights the value of Y-STR analysis in resolving sexual assault cases and provides the example of an 18-year old rape-murder cold case in Spain that was solved using Yfiler™ Plus chemistry.