Arguments for and Against Development of Genetic Finger Printing.

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Stuart Norris        Page         5/9/2007

Arguments for and Against Development of Genetic Finger Printing

The fingerprinting process uses enzymes to cut out specific sequences of DNA. The DNA is arrange in length order and labelled with a radioactive marker. These emit x-rays,  when the sample is photographed the markers can be seen. This produces the 'fingerprint' - a series of black lines corresponding to the DNA sequences present. Initially the DNA is removed from the sample cells by chemical methods, and the two strands of the double helix are separated. Restriction enzymes are then added. These identify a particular sequence and cut it away. This produces a mixture of free lengths of DNA. The next stage is to sort these sequences into length order. This is done using agarose gel electrophoresis. DNA is a charged molecule, so in an applied electric field it moves towards an electrode. The agarose gel slows down the larger molecules, but the shorter DNA strands move faster, so the process arranges the sequences in order. Acrylamide gel is sometimes used in a similar way for higher resolution ordering. Once the DNA sequences are ordered, chemical probes are added to the sample; like the restriction enzymes, these each select a particular sequence, and bind to it. As they contain radioactive atoms, when the sample is exposed to photographic film, these sequences will show up. An alternative method uses chemiluminescent labelling, where enzymes emit light by a chemical process. The whole process is repeated several times with different selections of enzymes, to build up a detailed fingerprint showing which DNA sequences are present. If a large number of sequences are used, and there is sufficient variation of the presence of these sequences among individuals within a population, then we have a unique profile of a single individual. 1342

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DNA fingerprinting has considerable advantages over conventional means of forensic crime detection. Conventional fingerprints attach only to hard surfaces, can be smeared, or avoided by the use of gloves. Even a clear print requires a significant degree of interpretation by investigating officers. The standard technique of comparing fourteen points between the print taken at the crime scene and the print of the accused has been subject to severe criticism. The novel ‘polymerase chain reaction’ (PCR) amplification technique facilitates an accurate DNA profile from very small amounts of genetic data. The fingerprint can be constructed not with standing contamination from oil, ...

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