DNA USED FOR IDENTITY

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
Is DNA effective in identifying persons?[answer provided by Daniel Drell of the U.S. DOE Human Genome Program]
DNA identification can be quite effective if used intelligently. Portions of the DNA sequence that vary the most among humans must be used; also, portions must be large enough to overcome the fact that human mating is not absolutely random.
Consider the scenario of a crime scene investigation . . .
Assume that type O blood is found at the crime scene. Type O occurs in about 45% of Americans. If investigators type only for ABO, finding that the "suspect" in a crime is type O really doesn't reveal very much.
If, in addition to being type O, the suspect is a blond, and blond hair is found at the crime scene, you now have two bits of evidence to suggest who really did it. However, there are a lot of Type O blonds out there.
If you find that the crime scene has footprints from a pair of Nike Air Jordans (with a distinctive tread design) and the suspect, in addition to being type O and blond, is also wearing Air Jordans with the same tread design, you are much closer to linking the suspect with the crime scene.
In this way, by accumulating bits of linking evidence in a chain, where each bit by itself isn't very strong but the set of all of them together is very strong, you can argue that your suspect really is the right person.
With DNA, the same kind of thinking is used; you can look for matches (based on sequence or on numbers of small repeating units of DNA sequence) at many different locations on the person's genome; one or two (even three) aren't enough to be confident that the suspect is the right one, but thirteen sites are used. A match at all thirteen is rare enough that you (or a prosecutor or a jury) can be very confident ("beyond a reasonable doubt") that the right person is accused.


DNA Fingerprint Identification
Summary DNA Fingerprinting, also known as Genetic Fingerprinting has recently come into vogue as a means of establishing personal identification. In the criminal justice system, DNA fingerprinting has been used with a degree of regularity over the past dozen years or so in order to establish personal identification in criminal matters. DNA has also been used in court paternity suits. DNA is an acronym for deoxyribonucleic acid, the substance that gives the human chromosome its shape.
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Simply stated, DNA is the blueprint of the body of every human being. The human body is made up of cells, each of which contains a nucleus. The nucleus is a special compartment that contains chromosomes which, in the human body, number forty-six. These chromosomes (23 from each parent) are composed of tightly wound up DNA molecules which lend each chromosome its unique characteristic shape. Each cell in the human body has the identical DNA makeup. Each DNA strand is composed of genes which determine a person's unique characteristics, such as body structure, or hair and eye color. There are no two humans with identical DNA compositions. The DNA is also inherited from the parents, and that is why the offspring so very often have a close physical resemblance to the parents. That DNA is inherited from parents is also the reason why DNA testing has proven to be useful in paternity suits. DNA fingerprinting dates back to 1985 when it was first developed in England by Sir Alec Jeffreys, and it has been considered the greatest achievement in forensic science since the development of fingerprinting as a means of personal identification more than one hundred years ago.
Although DNA was introduced as evidence in a criminal proceeding in 1985 and it played a role in the outcome of a trial in 1988, DNA fingerprinting did not capture the fancy of the public until it was used as evidence by the prosecution in the infamous O.J. Simpson trial (see below) in 1995 in Los Angeles Supreme Court, presided over by Judge Ito.Criminal Evidence DNA fingerprinting is so named because of its use as a means of identification of a subject. DNA fingerprinting technology continues to advance, and it can be used in criminal court cases because of the ability of crime scene investigators to obtain samples of DNA from clothing and objects and thus identify the source via DNA testing procedures. The analysts then match a number of DNA strands found at the scene of the crime to several DNA samples from the suspect in order to determine whether or not the DNA fingerprints belong to the suspect. Remarkably, around 30% of DNA fingerprinting has exonerated suspects of a crime. Additionally, DNA fingerprinting has been used to prove wrongful convictions in which persons serving sentences, most notably in crimes of rape, have been freed after substantial imprisonment time, following the submission of DNA evidence in a court appeal. DNA fingerprinting has also been used widely in the resolution of paternity cases. The Anna Nicole Smith case (see below) is one of the more famous court cases with the judgment of the court based on DNA fingerprinting.