Scientific evidence used in criminal cases and in paternity suits. DNA (deoxyribonucleic acid) molecules contain hereditary (genetic) information. The theory on which DNA testing is based consists of the following: all cells in the human body (except red blood cells) contain DNA; the structure of the DNA of a person is identical throughout a person's body; the DNA structure is constant from a person's infancy through their death; and, finally, that no two people (except identical twins) have the same DNA. DNA can be extracted from blood (white blood cells and plasma), skin, tissue, sperm, saliva, vaginal swabs, mouth scrapings, bones, and hair. The technique is widely accepted as scientifically reliable. While also known as "DNA fingerprinting," the process has nothing to do with fingerprints themselves but rather with the concept of uniqueness and the ability to link an individual to a crime (or establish paternity). It is a test of exclusion (proving that this could not have been the person) as well as a test which can include a person as one of a percentage of a population that could be the source. In the first case of a person convicted of a crime by DNA evidence (through semen recovered from a rape victim), bands from the defendant's blood and the semen "matched" and the probability of such a match occurring at random was 0.0000002 (or chance that it did not belong to the defendant was 1 in 833,333,333). 533 So. 2d 841. It is this last area-the probability calculation-that has received the most criticism. Some courts exclude such calculations. Criminal Law Bulletin vol. 27, no. 2 (March/April 1995).
At the risk of oversimplification, the following terms frequently are used when discussing DNA testing. The two main methods of DNA analysis are rflp and pcr. RFLP (restriction fragment length polymorphism) is a process that breaks DNA into small fragments at specific points on the DNA chain which are then measured. A newer method called PCR (polymerase chain reaction) can analyze as little as one-tenth of the biological material that is needed for RFLP. PCR is also able to give quicker results; however, the results are less discriminating. The PCR technique consists of extraction of the biological material, amplification (replication), and then typing. It is an in vitro process through which repeated cycling of the reaction reproduces a specific region of DNA, yielding millions of copies from the original. hla dq alpha (more commonly known as DQ Alpha) refers to the PCR method. HLA stands for human leukocyte antigen and DQ Alpha refers to the locus of the antigens. States are increasingly requiring mandatory submission of blood samples from certain convicted persons for DNA identification and placement in an information bank which can then be used in the event that future crimes are committed. See Cal. Penal Code 290.2; Fla. Stat. Ann. 943.325.
