Forensic DNA Analysis

Forensic DNA analysis is used to identify individuals using genetic samples. Basically, the system uses a set of identifying numbers to match two different samples. The concept was first designed by Sir Alec Jeffreys at the University of Leicester in 1985. Today, it is a standard practice in conducting investigations for crimes such as murder and rape.

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

History of Forensic DNA Analysis
DNA typing, since it was introduced in the mid-1980s, has revolutionized forensic science and the ability of law enforcement to match perpetrators with crime scenes. Thousands of cases have been closed and innocent suspects freed with guilty ones punished because of the power of a silent biological witness at the crime scene.

'DNA fingerprinting' or DNA typing (profiling) as it is now known, was first described in 1985 by an English geneticist named Alec Jeffreys. Dr. Jeffreys found that certain regions of DNA contained DNA sequences that were repeated over and over again next to each other. He also discovered that the number of repeated sections present in a sample could differ from individual to individual. By developing a technique to examine the length variation of these DNA repeat sequences, Dr. Jeffreys created the ability to perform human identity tests.

How DNA Profiling Helps to Solve Crimes
DNA profiling or fingerprinting was developed in 1984 by British geneticist Sir Alec Jeffreys and first used in forensic science to convict Colin Pitchfork in the 1988 Enderby murders case.

A DNA fingerprint is the same for every cell, tissue and organ of a person. This DNA fingerprint cannot be altered by any known treatment.

It makes sense that DNA evidence has become such a powerful crime solving tool because no person's DNA fingerprint is the same except for identical twins. This means that DNA collected from a crime scene can either link a suspect to the evidence or eliminate them which is why accurate DNA fingerprinting is critical as a crime solving tool.



Collecting DNA Evidence at a Crime Scene
DNA evidence can be collected from virtually anywhere at a crime scene. DNA has helped solve many cases when imaginative investigators collected evidence from non-traditional sources:

A masked rapist was convicted of forced oral copulation when his victim's DNA fingerprint matched DNA evidence swabbed from him.
Many cases have been solved by DNA analysis of saliva on cigarette butts, postage stamps, rims of cups and glasses.
DNA analysis of a single hair found deep in the victim's throat provided a critical piece of evidence to solve the crime and apprehened the criminal.

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. All DNA profiles stored in CODIS are generated using STR (short tandem repeat) analysis.

Some Interesting Uses of DNA Forensic Identification

Identifying September 11th Victims
Identifying the victims of the September 11, 2001, World Trade Center attack presented a unique forensic challenge because the number and identity of the victims were unknown and many victims were represented only by bone and tissue fragments. At the time of the attack, no systems were in place for rapidly identifying victims in disasters with more than 500 fatalities. The National Institutes of Justice assembled a panel of experts from the National Institutes of Health and other institutions to develop processes to identify victims using DNA collected at the site. Panel members produced forms and kits needed to enable the medical examiner’s office to collect reference DNA from victims’ previously stored medical specimens. These specimens were collected and entered into a database. The medical examiner's office also received about 20,000 pieces of human remains from the World Trade Center site, and a database of the victims’ DNA profiles was created.

To avoid contamination of evidence that may contain DNA, always take the
following precautions:
Wear gloves. Change them often.
Use disposable instruments or clean
them thoroughly before and after handling
each sample.
Avoid touching the area where you believe
DNA may exist.
Avoid talking, sneezing, and coughing
over evidence.
Avoid touching your face, nose, and mouth
when collecting and packaging evidence.
Air-dry evidence thoroughly before
packaging.
Put evidence into new paper bags or
envelopes, not into plastic bags. Do not
use staples.