DNA testing methods for evidence in cases of sexual assault focus on the isolation of sperm cells. The differential DNA extraction method involves the differential lysis of epithelial and sperm cells resulting in two separate DNA sample fractions. This method allows for the separation of epithelial DNA and sperm cells prior to their lysis. The traditional differential DNA extraction method is labor intensive, time consuming, not amenable to automation, and can yield mixed DNA profiles in the resulting fractions due to incomplete separation of the different cell types.
The goal of this project is to develop and evaluate a modified differential DNA extraction method expedited by the Costar® Spin-X® centrifuge tube filter in conjunction with the Hamilton MICROLAB® STARlet® and the Promega DNA IQ™ System to increase sexual assault evidence processing and throughput. The DNA section of the Denver Crime Laboratory has been processing sexual assault evidence using a male screen procedure followed by a traditional differential DNA extraction for samples suspected of containing semen. The male screen procedure is a highly sensitive assay and enhancements to the procedure have made it highly effective for detecting male DNA and identifying samples suitable for male-specific Y-chromosome STR DNA analysis. The traditional differential DNA extraction, however, is a manually performed Chelex extraction and is a labor intensive and less sophisticated DNA extraction procedure than an automated magnetic bead extraction. The manual differential DNA extraction requires post-extraction processing to achieve similar sample quality as samples processed using the Promega DNA IQ System on the Hamilton STARlet during the male screen procedure. This study is designed to evaluate the use of the Spin-X tube filter for an optimized differential DNA extraction method that will combine the male screen and traditional differential DNA extraction procedures used at the Denver Crime Laboratory.