DNA Fingerprinting and its application

DNA (Deoxyribonucleic acid) is a long polymer of deoxyribonucleotides. It is the genetic material that transfers hereditary information from one generation to the next generation. It is specific to an individual. Every organism on this earth has its own peculiar DNA which doesn’t match with any other organism except identical twins. This characteristics of DNA enable scientist to start DNA Fingerprinting for the identification of an individual. Our DNA doesn’t match with any other person but it is little bit similar to that of our parents and siblings. The chemical structure of DNA of every individual is same. The only in people is the order of base pair. There are so many millions of base pairs in each individual’s DNA that every person has a different sequence. Using this sequences, every person could be identified solely by the sequence of their base pairs. However, there are so many millions of base pairs due to which the task would be very time-consuming and expensive. Every DNA strand has stretches that contain genetic information which are responsible for an organism’s development called exons and stretches that apparently supply no relevant genetic information at all are called introns. Although the introns seems useless, it has been found that they contain repeated sequences of base pairs. These base sequences are called VARIABLE NUMBER TANDEM REPEATS (VNTRs). VNTRs are called minisatellites were discovered by Alec Jeffreys of U.K.

The southern Blot is a process by which genetic patterns can be analysed which appears in a person’s DNA (Deoxyribonucleic acid). It was devised by E.M. Southern in 1975 for separating DNA fragments. This process involves the following steps:

v Isolating the desired DNA: It can be done either chemically or by using detergent to wash the extra material from the DNA or mechanically by applying a large amount of pressure in order to squeeze out the DNA or by refrigerated ultracentrifugation. If the amount of DNA is less, the DNA can be increased by PCR (Polymerase Chain Reaction).

v Cutting of DNA: DNA is cut into several pieces of different size. This is done by using restriction enzymes.

v Sorting of DNA: The small pieces of DNA are sorted according to their size. This is done by gen electrophoresis process. The DNA is poured into a gel such as agarose and electric charge is applied to the gel with the positive charge at the bottom and negative charge at the top. The pieces of are get attracted towards the bottom of the gel because of its slightly negative charge. The smaller pieces, however, move more quickly towards bottom than the larger pieces. The different sized pieces of pieces of DNA is separated with the smaller pieces towards bottom and the larger pieces towards the top.

v Denaturing the DNA fragments: Chemical structure of DNA is distorted so that the DNA is rendered single stranded. This is done either by heating or chemically treating the DNA in the gel using alkali.

v Blotting the DNA: The gel with the size-fractionated DNA is applied to a sheet of nitrocellular paper or nylon membrane and then baked to permanently attach the DNA to the sheet. The Southern Blot is now ready to be analysed.

In order to analyse a Southern Blot, a radioactive genetic probe is used in a hybridization reaction with the DNA in question. If an X-ray of Southern Blot is taken after a radioactive probe has been allowed bound with the denatured DNA on the paper sheet, only the areas where the radioactive probe binds will show themselves on the film (autoradiography). This allows the researcher to identify the occurrence and frequency of the particular genetic pattern contained in the probe of a person’s DNA.

APPLICATIONS OF DNA FINGERPRINTING:

v TO SOLVE DISPUTED PATERNITY AND MATERNITY: It is used to solve cases of disputed paternity and maternity as a person inherit his/her VNTRs from his/her parents. It is very important application in this era because nowadays the cover page of most of the newspapers is occupied by this type of news. Many times a man get involved in relation with a girl and start mating with her but after she became pregnant, the man left her and run away even doesn’t accept the baby to be his own. This technique can solve all such problems.

v TO IDENTIFY CRIMINALS: It is proved that our body shed off hairs randomly and it became the weakness for criminals. A criminal may be very clever but his/her hair will shed off from body parts without his/her concern or sometime get injured accidentally. The DNA isolated from hair, blood, skin cells or other genetic evidence left at the crime scene is compared through VNTR patterns, with the DNA of all the criminal suspects to determine guilt or innocence.

v PERSONAL IDENTIFICATION: The notion of using DNA Fingerprints as a sort of genetic bar code to identify individual has been discussed but this is not likely to happen anytime in the near future. This technology required to isolate, keep on file and then analyse millions of very specified VNTR patterns is both expensive and impractical.

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