DNA Analysis Definition

Model of the DNA molecule

DNA analysis, or DNA fingerprinting, is a forensic test used to determine whether a suspect's DNA is present at a crime scene.

DNA as identification

Almost every part of each strain of human DNA is the same. However, except for identical twins, everyone on earth has certain unique features in their DNA, which can be used as a form of identification.

History

The first DNA analysis technology was restriction fragment length polymorphism (RFLP); later, polymerase chain reaction (PCR) allowed the use of very small DNA samples. The FBI standard today is short tandem repeat (STI) analysis.

STI analysis

STI analysis uses 13 portions, or loci, of the human genome. The odds that two unrelated people would have the same DNA in all 13 loci are about 1 in a billion.

CODIS

The Combined DNA Index System (CODIS) keeps a record of the STI loci for those convicted of violent or sex crimes. If one of these convicts later leaves DNA at a crime scene, it may be used at trial as evidence.

Other Techniques

Mitochondrial DNA analysis uses DNA from sources that can't be used in STI analysis. Y chromosome analysis allows separation of multiple DNA contributors in a sample.

References

• "Using DNA to Solve Cold Cases." U.S. Dept. of Justice Special Report, July 2002.
• T. O'Connor. "DNA Analysis: Typing and Identification," 2006. MegaLinks in Criminal Justice.

Resources

• Gerald J. Turetsky. "Take DNA When You Can." New York Times, April 9, 2006.