Dna Fingerprinting
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DNA FINGERPRINTING
DNA fingerprinting is a method of identification that compares fragments of deoxyribonucleic acid. It is a technique used to distinguish between individuals of the same species by using only samples of their DNA. It is also called DNA typing. DNA is the genetic material found within the cell nuclei of all living things. In mammals, the strands of DNA are grouped into structures called chromosomes. Unless dealing with identical twins, the complete DNA of each individual is unique. Over 99% of all 3 billion nucleotides in human DNA, which we inherit from each parent, are identical among individuals. However, for every 1000 nucleotides that we inherit there is one site of variation or polymorphism, in the population. These DNA polymorphisms change the length of the DNA fragments produced by the digestion of restriction enzymes. The resulting fragments are called restriction fragments length polymorphisms (RFLPs or “riflips”). The exact number and size of fragments produced by a specific restriction enzyme digestion varies from individual to individual.
DNA fingerprinting was first developed as an identification technique in1985. Sir Alec Jeffreys at the University of Leicester invented it. At first, DNA fingerprinting was used to detect the presence of genetic diseases but soon came to be used in criminal investigations and forensic science. It matches suspects to samples of blood, hair, saliva, or semen. It has also led to several exonerations of formerly convicted suspects. It is also used in such applications as studying populations of wild animals, paternity testing, identifying dead bodies, and establishing the composition of foods. It has also been used to generate hypotheses on the pattern of the human dispersion in prehistoric times. The first criminal conviction based on DNA evidence in the United States happened in 1988. Generally, courts have accepted the reliability of DNA testing and admitted results into evidence. Testing is subject to the legal code of the jurisdiction in which it is performed. Usually testing is voluntary, but it can be made compulsory with a warrant or court order. Several jurisdictions have begun to assemble databases containing DNA information of convicts. The United Kingdom has the largest DNA database in the world which holds over two million records.
There are several methods of DNA fingerprinting. The nmost prevalent today is based on polymerase chain reaction (PCR). This method uses short tandem repeats (STR). This method uses highly polymorphic regions that have short repeated sequences of DNA. These STR locations are targeted with sequence- specific primers and are amplified using PCR. The DNA fragments that result are then separated and detected using electrophoresis.