DNA Extraction and Quantification
DNA profiling begins with extracting DNA from biological evidence—blood, saliva, semen, hair roots, skin cells, or bone. Organic extraction uses detergent to lyse cells, proteinase K to digest proteins, and phenol-chloroform to separate DNA from cellular debris. Solid-phase extraction using silica-coated magnetic beads is now more common in automated high-throughput laboratories. After extraction, DNA is quantified using real-time PCR (qPCR) with human-specific primers to determine the amount of amplifiable human DNA present and detect the presence of male DNA (useful in sexual assault cases). Typical forensic samples contain 0.1-100 nanograms of DNA—far less than the microgram quantities in research settings, requiring exquisitely sensitive techniques.