The use of DNA probes and the development of retrieval techniques have made it possible to match DNA molecules to one another for identification purposes. This process has been used in a forensic procedure called DNA fingerprinting.
DNA fingerprinting depends on the presence of repeating base sequences that exist in the human genome. The repeating sequences are called restriction fragment length polymorphisms (RFLPs). As the pattern of RFLPs is unique for each individual, it can be used as a molecular fingerprint.
To perform DNA fingerprinting, DNA is obtained from an individual's blood cells, hair fibers, skin fragments, or other tissue. The DNA is then extracted from the cells and digested with enzymes. The resulting fragments are separated by a process called electrophoresis. Electrophoresis is a process in which electrical charges separate DNA fragments according to size. The separated DNA fragments are then detected with DNA probes and used to develop a fingerprint. A statistical evaluation enables the forensic pathologist to compare a suspect's DNA with the DNA recovered at a crime scene and to state with a high degree of certainty (usually 99 percent) that the suspect was at the crime scene.