DNA Profiling (Fingerprinting)
DNA is the master molecule of all life forms. It constitutes the blue prints of every living organism through which characters are passed generation to generations. However, every living organism differs only due to nucleotide sequences of chromosome. The nucleotides form codes; therefore, this coded genetic informations can be profiled to produce most authentic identity card of any organism. The complicated technology that facilitates the identification of individuals at genetic level is known as DNA fingerprinting or more specifically DNA profiling. This genetic analysis is based on identifying tiny segments of the hereditary material which testify the unique molecular signature which cannot be altered. With the help of DNA profiling technology identity of burnt or unidentifiable dead body can be done.
The basic requirements for DNA profiling is the availability of biological samples which can be anything including blood stains, a piece of hair with its root, few drops of semen, skin cells, a mouth swab, cells of bone marrow of any body tissue.
In 1984, for the first time, a British geneticist, Alec Jeffreys working at the University of Leicester developed the technique of DNA fingerprinting. This method has been patented, and being used in Europe and America. Its success is based on. identification of small segment of DNA which testifies the unique molecular signature that every person on earth possesses and which cannot be changed in ones life time.
It is important to note that 99% of base sequences is the same in the DNA of all human beings. Only a short stretches of sequences which is about 3 billion base pairs, differ person to person. Out of the total DNA, about one in 1000 base pairs is a site of variation in the population. This is an unusual sequence of bases of 10-15 base pairs long which is repeated several times. These bases were first isolated and identified by A. Wyman and R. White in 1980 at the University of Utah as hypervariable segments of DNA and termed as 'variable number of tandem repeats' (VNTRs). On the basis of number of repeats present in VNTRs, the length of segment is measured. In different person the length of VNTR differs and, therefore, VNTR is the key of DNA fingerprinting.
It was Jeffreys who first used VNTRs in forensic science. The VNTRs act as genetic markers. The scheme developed by Jeffreys for measuring the length of fragments of DNA containing the repeated sequences is also known as 'restriction fragment length polymorphism' (RFLP) testing.