How does forensic identification work?

Any type of organism can be identified by examination of DNA sequences unique to that species. Identifying individuals within a species is less precise at this time, although when DNA sequencing technologies progress farther, direct comparison of very large DNA segments, and possibly even whole genomes, will become feasible and practical and will allow precise individual identification.

To identify individuals, forensic scientists scan 13 DNA regions, or loci, that vary from person to person and use the data to create a DNA profile of that individual (sometimes called a DNA fingerprint). There is an extremely small chance that another person has the same DNA profile for a particular set of 13 regions.

Some Examples of DNA Uses for Forensic Identification
• Identify potential suspects whose DNA may match evidence left at crime scenes
• Exonerate persons wrongly accused of crimes
• Identify crime and catastrophe victims
• Establish paternity and other family relationships
• Identify endangered and protected species as an aid to wildlife officials (could be used for prosecuting poachers)
• Detect bacteria and other organisms that may pollute air, water, soil, and food
• Match organ donors with recipients in transplant programs
• Determine pedigree for seed or livestock breeds
• Authenticate consumables such as caviar and wine

DNA Forensics Databases

National DNA Databank: CODIS

The Combined DNA Index System, CODIS, blends computer and DNA technologies into a tool for fighting violent crime. The current version of CODIS uses two indexes to generate investigative leads in crimes where biological evidence is recovered from the crime scene. The Convicted Offender Index contains DNA profiles of individuals convicted of felony sex offenses (and other violent crimes). The Forensic Index contains DNA profiles developed from crime scene evidence.

CODIS utilizes computer software to automatically search its two indexes for matching DNA profiles. Law enforcement agencies at federal, state, and local levels take DNA from biological evidence (e.g., blood and saliva) gathered in crimes that have no suspect and compare it to the DNA in the profiles stored in the CODIS systems. If a match is made between a sample and a stored profile, CODIS can identify the perpetrator.

As more offender DNA samples are collected and law enforcement officers become better trained and equipped to collect DNA samples at crime scenes, the backlog of samples awaiting testing throughout the criminal justice system is increasing dramatically.

Advantages
• Major crimes often involve people who also have committed other offenses. Having DNA banked potentially could make it easier to identify suspects, just as fingerprint databases do.
• Innocent people currently are incarcerated for crimes they did not commit; if DNA samples had been taken at the time of arrest, these individuals could have been proven innocent and thereby avoided incarceration..
• Banking arrestees’ DNA instead of banking only that of convicted criminals could result in financial savings in investigation, prosecution, and incarceration