DNA ‘fingerprints’ are signature pieces of DNA that are specific to an individual, and therefore, can be used to identify a person.
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Nearly every cell in the human body contains DNA. While almost all of the human DNA sequence is identical to every other person on the planet, 0.1% of it is unique to the individual. This 0.1% equates to roughly three million base pairs and the unique patterns amongst these base pairs distinguish an individual from another.
In 1980, minisatellites were first discovered, these are short sequences of repetitive DNA which vary greatly between individuals, differences in short 10-60 base pairs long sequences has subsequently formed the basis of DNA fingerprinting.
How DNA fingerprinting works
To implement DNA fingerprinting, a sample of DNA is required, which can be provided in the form of blood, cheek swabs, saliva, other bodily fluids and sometimes hair.
There are several methods of DNA fingerprinting using either polymerase chain reaction (PCR), restriction fragment length polymerization (RFLP), amplified fragment length polymorphism (ampFLP) and investigation of short tandem repeats (STR). Most recently there has been the development of next-generation sequencing which may also be used.
In brief, RFLP uses restriction enzymes to fragment the DNA, these act like molecular scissors to cut the DNA strands into much smaller pieces. Gel electrophoresis then separates the fragments in order of their size.
The fragments are tagged with a radioactive marker and visualized using x-rays to produce an autoradiograph.
PCR amplifies the regions of interest in the DNA and can be used to identify samples from the same individual. AmpFLP is a combination of both RFLP and PCR. STR investigates the DNA at 13 specific sites for the number of repeats present.
NGS uses DNA fragments, sequences these with a direct readout eliminating the need for further detection methods.
Why is DNA fingerprinting useful?
There are several major applications of DNA fingerprinting. Most notably in forensic investigations for a variety of reasons such as; confirming the identity of a body, implicating a perpetrator in a crime or clearing a suspect.
DNA evidence can often be the essential piece of evidence that leads to a conviction of a crime. DNA evidence has also been instrumental in exonerating innocent people who had been incarcerated for crimes they did not commit.
The first case of DNA exoneration in the US took place in 1989 and since then, according to the Innocence Project, a total of 367 people have been exonerated due to DNA evidence and a total of 162 actual assailants have been identified and incarcerated.
Another important use of DNA fingerprinting is in determining the relationship of one person to another. In order to establish paternity, confirm relative's parents of adopted children within family disputes and family law and to establish familial relationships to settle cases of inheritance.
DNA fingerprinting has a variety of benefits within medicine. Currently, DNA fingerprinting is used to compare patients awaiting transplants with potential donors to find appropriate genetic matches. DNA fingerprinting is being used to develop personalized treatments for patients with cancer, an area that is expected to show continued advancements.
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