Forensics is the use of scientific techniques in criminal investigations. DNA profiling (also known as DNA analysis, DNA or genetic fingerprinting, DNA testing and DNA typing) has revolutionized criminal forensics. While the use of these terms is common, few understand what they refer to beyond being a laboratory method of identification.
What are the basics of DNA?
DNA is the abbreviation for deoxyribonucleic acid. This is a material that reproduces an exact copy of itself and is found in almost all forms of life. DNA is the main part of chromosomes. These are threadlike strands of protein and nucleic acids that carry genetic information. They are found in every molecule of DNA as a pair of strands that coil around each other similar to a spiraling ladder. Chemical groups found in specific pairs, or bases, form the rungs of this ladder. The bases on one side are complementary to those on the other. The genetic information is the sequence of these bases.
How do DNA profiling and DNA databases aid law enforcement?
Merely 0.1% of DNA differs between individuals. Technicians can use such variable regions in generating a DNA profile of a person. Sources for DNA are typically blood, saliva, and hair. Other body products, tissues, and even bone can serve as a source. DNA profiling takes place when body fluids or tissue samples undergo analysis for identification of individuals. It is not necessary for comparison samples to be of the same material as all cells of one person have identical DNA. While DNA analysis is time-consuming, it yields the most accurate scientific evidence available. The odds that DNA matches are incorrect can be narrowed to millionths of a percent.
While criminal investigations generally involve comparing DNA samples from evidence obtained at the scene with that of a specific set of DNA regions of a known suspect, comparison is increasingly being seen with DNA databases, a structured set of computerized data. Much like fingerprints of suspects being compared with those of known criminals that authorities maintain on file, the databases contain DNA profiles at all government levels. This affords a significant tool to investigators and prosecutors. Because criminals are frequently recidivists and likely to repeatedly violate the law, these are DNA profiles of potential suspects with which DNA evidence may be compared and lead to a conviction.
How is DNA a practical tool for prosecution?
Dr. Alec Jeffreys first discovered that each individual carries a genetic fingerprint in their DNA in 1985. Shortly afterward it was used not only to achieve a conviction of the perpetrator of a double homicide, but the exoneration of an innocent individual in that same crime. The United States first saw successful use of DNA evidence in prosecution of a Florida rapist in 1987. In the nearly quarter century since it has come to revolutionize law enforcement investigations and prosecutions in many ways including:
- identification of crime victims
- establishment of paternity relationships in sexual battery cases
- aid in identification and elimination of possible suspects given potential DNA matches with crime scene evidence
- exoneration of individuals wrongly accused or convicted of criminal activity
- identification of protected species in prosecution of poachers
An invaluable law enforcement tool
In a manner similar to how fingerprinting began to advance police investigation beginning in the 1890s, DNA profiling has been even more effective a century later. The DNA profile serves as a genetic fingerprint found in each individual that provides the ability to distinguish all but identical twins from each other. Evidence collection methods have been advanced in recent years and DNA analysis now serves as an invaluable tool in successful law enforcement and prosecution.
Source:
"Advancing Criminal Justice Through DNA Technology" DNA.gov: Basic Biology of DNA
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