Dna Fingerprinting and Forensics
DNA fingerprinting is the overall term applied to a range of techniques that are used to show similarities or dissimilarites between the DNA present in different individuals of the same or different species.
The DNA fingerprinting technique was pioneered by Alec Jeffreys in 1985. By looking at small samples of bodily tissues, a pattern can be produced by digesting the DNA using a series of enzymes known as restriction enzymes, or restriction endonucleases. This digested material is then placed on a sheet of agarose gel, and the fragments are separated by passing an electric current across the gel. Different enzymes produce different banding patterns and normally several enzymes are used in conjunction to produce a high definition digestion. Because these digestions of DNA are particular to an individual they are known as DNA fingerprints. These tests can be carried out on small pieces of material due to DNA amplification techniques. Different combinations of enzymes produce different restriction patterns and the likelihood of a match between the test DNA and an individual differs.
When the digested DNA is placed into the agarose gel comparative samples of DNA are also loaded on the gel. These other samples may be test samples or they may be controlled samples, because it is vital to always include a standard piece of DNA to calibrate the results. The loaded gel is then placed in a liquid bath and an electric current is passed through the system. The fragments of DNA are of different sizes and different electrical charges. As a result, the fragments migrate down the gel in various distances. The DNA can be seen by the application of dye, producing a gel which has a series of lines showing where the DNA has migrated. The enzymes used for the digestion cut at specific locations and different-sized fragments are produced depending on the bases (that is, the particular sequence of nucleotides) present in the DNA. Fragments of the same size in different lanes indicate the DNA has been broken into segments the same size. This indicates homology between the sequences under test. The greater the number of enzymes used in the digestion, the finer the resultant resolution.
DNA fingerprinting is used in forensics to examine DNA samples taken from a crime scene and compare them to those of a suspect. The statistical chance of two samples of DNA producing identical digestion patterns different individuals is very small; sometimes less than one against more than the population of humans who have ever existed.
DNA fingerprinting is now an import weapon n the arsenal of forensic chemists.
Although DNA fingerprinting is scientifically sound and is increasingly gaining acceptance in courtroom proceedings, because modern genetics is poorly understood by the general population, the use of DNA fingerprinting in courtrooms remains controversial. Jurors who are ignorant of science, especially the principles of modern genetics, are often easily confused by lawyers uninterested in scientific truth but who are, instead, interested only in obtaining a desired verdict. There are, however, legitimate concerns regarding the data collection and laboratory procedure that may impact the DNA fingerprinting procedures. In additional, because the chance of a match is given as a statistical likelihood there are concerns that insufficient DNA fingerprint tests have been carried out to eliminate chances of a false match with absolute certainty. In the United States, however, the standard for conviction in a criminal trial is proof "beyond a reasonable doubt" and there is no requirement for absolute certainty. In civil trials (i.e., paternity suits, etc.) the standard is even lower, requiring only "a preponderance of the evidence" (more than 50/50 probability), to render a decision in favor of the party bringing the lawsuit (plaintiff). Regardless, the scientific evidence is overwhelming that DNA fingerprinting, when properly conducted, more than meets the burden of proof for civil and criminal trials.
This is the complete article, containing 635 words
(approx. 2 pages at 300 words per page).
