CODIS (Forensic Science)
The Combined DNA Index System, better known as CODIS, was established as the result of a suggestion from the Technical Working Group on DNA Analysis Methods; the intent was to create a national database of DNA (deoxyribonucleic acid) profiles collected from convicted criminals. When CODIS was initiated in 1990 as a pilot project of the Federal Bureau of Investigation (FBI), it included fourteen state and local laboratories.
The DNA Identification Act of 1994 allowed the formation of a national DNA database and clarified which types of DNA evidence could be stored in it. DNA profiles from persons convicted of crimes, evidentiary items obtained from crime scenes, and unidentified human remains were to be included, as well as profiles voluntarily submitted by relatives of missing persons. In 1998, the national database became operational, and by 2003 it was accepted by all fifty states. Qualified city, county, regional, state, and federal crime laboratories, as well as labs in several in other countries, now contribute to this powerful crime-solving tool.
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Structure of the Database (Forensic Science)
CODIS is operational at three tiers: the National DNA Index System (NDIS), the State DNA Index System (SDIS), and the Local DNA Index System (LDIS) levels. A DNA profile originates locally and then migrates to the state and national levels. This approach allows each state access to a database that is concurrent with its individual legislation, including what crimes will result in submission of a DNA profile (for example, sexual assault, any violent crime, all felonies).
CODIS consists of two main databases: the forensic index and the convicted offender index. The forensic index contains data on DNA profiles obtained from victims or crime scenes, whereas the convicted offender index includes the profiles of those convicted of offenses. Using the two indexing systems, it is possible to link crimes together for the purpose of identifying a repeat perpetrator or to link a crime to a person who is or was in prison. Other databases existing in CODIS include the arrestees index, the missing persons index, the unidentified human remains index, and the biological relatives of missing persons index. Whether an individual state participates in these at the national level depends on state policy or law. In order for a state to be eligible to participate in CODIS, the appropriate state authority must sign a memorandum indicating that the state’s laboratory (or laboratories) adheres to FBI quality assurance standards; the...
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Putting a DNA Sample Through CODIS (Forensic Science)
DNA samples can be taken from convicted persons in several different ways. Blood or buccal swabs (swabs of the inside of the cheek) are generally collected, although in theory almost any tissue could be used. Forensic samples come from a huge variety of sources, the most common being semen from sexual assault cases, but blood, hair, saliva, bone, or virtually any other tissue or body fluid can be tested. New developments have allowed for touch samples—samples extracted from items that have come into direct contact with the persons of interest (such as held objects)—to be used also as potential sources of profiles.
DNA profile information is submitted to CODIS in the form of short tandem repeats (STRs). Thirteen core STR loci were chosen for use with CODIS; the profiles of convicted offenders must contain all thirteen of these loci to be uploaded to CODIS, whereas forensic profiles, which often originate from less-than-ideal sources, are required to have at least ten loci.
At the local level, analysts have some leeway when searching the database. For instance, a laboratory may require that a complete match be made at a locus for that locus to be considered, whereas another laboratory, recognizing that degraded DNA from a crime scene can result in the loss of part of a profile, might find a partial profile probative. Likewise, the minimum number of loci needed to be considered informative can vary...
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Further Reading (Forensic Science)
Balding, D. J., and P. J. Donnelly. “Evaluating DNA Profile Evidence When the Suspect Is Identified Through a Database Search.” Journal of Forensic Sciences 41 (1996): 603-607. Leads the reader through the process of entering a DNA profile into a database and discusses the population genetics associated with such a profile.
Butler, John M. Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers. 2d ed. Burlington, Mass.: Elsevier Academic Press, 2005. Provides a detailed overview of short tandem repeats and their applicability to forensic science.
Houck, Max M., and Jay A. Siegel. Fundamentals of Forensic Science. Burlington, Mass.: Elsevier Academic Press, 2006. Good general textbook includes discussion of DNA analysis.
National Research Council. The Evaluation of Forensic DNA Evidence. Washington, D.C.: National Academy Press, 1996. Spells out the guidelines on methods of DNA analysis that are accepted in the courtroom.
Walton, Richard H. Cold Case Homicides: Practical Investigative Techniques. Boca Raton, Fla.: CRC Press, 2006. Examination of cold cases includes a section on applying CODIS to the investigation of old, unsolved crimes.
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