DNA extraction from hair, bodily fluids, and tissues.

When biological materials that have been found at crime scenes—such as hairs, bodily fluids, and tissues—are submitted for DNA (deoxyribonucleic acid) analysis, the samples must first undergo DNA extraction procedures. The most common methods for extracting DNA from such materials are organic extraction, Chelex extraction, extraction using preservation paper, and extraction using silica-based columns. The common organic extraction uses detergent and proteinase to break open (lyse) cells, followed by introduction of an organic solvent to separate proteins and other cellular debris away from the DNA. Chelex extraction is a quick and easy procedure, but the purity of the DNA extracted is low. Chelex binds metal ions that could otherwise lead to poor DNA typing results, but little other purification is done. Preservation papers provide another quick method for extracting DNA. Bodily fluids are applied directly to the paper, where the cells are immediately lysed. Once the sample is dried, a small portion can be punched out, washed briefly, and then moved directly to DNA amplification. Silica-based columns bind DNA following cell lysis, allowing cellular debris to be washed through. The DNA is then eluted in relatively pure form.