A novel three‐step DNA extraction method for mixed bloodstains

Abstract

Mixed DNA samples from at least two contributors can be present at a crime scene, which could be the most crucial piece of genetic evidence. The mixed stains in sexual assault cases are typically separated using differential lysis procedures (a two‐step method). Blood mixed stains, however, are usually difficult to separate. In this work, we propose that a mixed stain comprises three layers, that is, (1) the upper layer which is primarily made up of cells from one contributor; (2) the middle layer which is a similar mixture from two contributors; and (3) the lower layer which primarily comprises cells from the other contributor. Based on this concept, a novel three‐step DNA extraction method was proposed to solve the challenge involving bloodstains from two contributors. In the experiment, we extracted three layers DNA from mixed bloodstains using three steps. As a result, single‐source DNA and approximate single‐source DNA were detected from steps 1 and 3, respectively. This study demonstrates that the DNA from some mixed blood stains could be effectively separated following an appropriate extraction strategy, providing valuable insights, and serving as a reference for future examination of blood mixtures.