Definition of DNA Fingerprinting
DNA fingerprinting is a scientific process in which samples of DNA (deoxyribonucleic acid) are collected and either compared to DNA evidence collected at a crime scene or stored away for possible future use. DNA, defined by Encarta as "the genetic material found within the cell nuclei of all living things," is unique to each individual, except in the case of identical twins.
Other People Are Reading
-
Forensic Applications
-
Because the DNA structure, or genetic makeup, of each individual is different, except in identical twins, a DNA sample that matches DNA collected at a crime scene is considered very compelling evidence that the individual with that DNA was present at the scene at some time. It does not, however, conclusively prove that a crime was committed by that person. Matching stored DNA fingerprints to DNA samples collected at the scenes of major disasters is one means of identifying victims of the disaster.
Collection of DNA
-
A DNA sample can be extracted from body tissue or fluid, such as hair, semen, saliva or blood. One of the most common methods of obtaining a DNA sample is by swabbing the inside of a subject's cheek. The sample then is processed to create a DNA profile. While the great majority of DNA is identical in all humans, roughly 3 million base pairs of DNA---amounting to only 1/10 of 1 percent of each human genome---are unique, according to Teachers' Domain. It is that tiny segment of the DNA that makes it possible to distinguish one individual from billions of others.
-
Profiling Process
-
Samples of DNA collected as evidence and from possible suspects are processed into DNA profiles in the laboratory. First, the sample is broken into segments using enzymes. A process called electrophoresis then is used to arrange the segments by size. Then, Encarta explains, "the segments are marked with probes and exposed on X-ray film, where they form a characteristic pattern of black bars---the DNA fingerprint."
Types of DNA Analysis
-
There are five methods of analyzing DNA samples, and the decision about which to use is often dictated by the quantity and quality of the samples available for testing. The DNA Initiative is a U.S. government program to promote the use of DNA evidence as an investigative tool. It identifies the methods of analyzing DNA as RFLP (restriction fragment length polymorphism), PCR (polymerase chain reaction), STR (short tandem repeat), mitochondrial and Y-chromosome. While RFLP analysis requires a DNA sample roughly the size of a quarter, PCR analysis is possible with the DNA available in a few skin cells.
Use as Evidence
-
Courts in the United States and many other countries today accept DNA evidence, although its use still remains somewhat controversial, in part because DNA fingerprinting utilizes only selected segments and not complete strands. The increasing use of DNA evidence has led local, state and federal authorities to build databases of DNA profiles, including DNA samples from convicted offenders. The U.S. national DNA database, established by the Federal Bureau of Investigation, is known as CODIS (Combined DNA Index System).
-
