DNA fingerprinting however is still quite controversial when used to solve crimes. Courts oftenreject DNA tests that show guilt because the scientists disagree about how to calculate the odds that the cells from the crime scene and the suspects cells match. Also legal experts have argued that DNA evidence can be so overwhelming to the jury, that it swamps all other arguments giving a defendant an unfair trial.
METHODS OF FINGERPRINTING
There are two ways to determine if two samples of DNA are matches, the Polymerase Chain Reaction (PCR),
and the Restriction Fragment Link Polymorphism (RFLP). Both of these methods were used in the O.J. Simpson case.
The RFLP method is an older method than the PCR method. For the RFLP method
a larger sample of cells is needed, and it takes longer, but the results are no less accurate than the PCR method.
"RFLP is a technique in which organisms may be differentiated by analysis of patterns derived from cleavage of their DNA. If two organisms differ in the distance between sites of cleavage of a particular restriction endonuclease, the length of the fragments produced will differ when the DNA is digested with a restriction enzyme. The similarity of the patterns generated can be used to differentiate species (and even strains) from one another."PCR is a newer, faster way of DNA Fingerprinting. It uses only 30-50 cells,(1/200th of amount needed for RFLP)which can be degraded. PCR is better at proving suspects innocent that guilty, because if there are no errors in the lab, and cells found at the crime scene do not match those of the defendant, the defendant is innocent. However, if the suspects DNA does match the incriminating DNA found at the scene, there is still a 1 in 21 chance the suspect really is innocent and there is someone elso with the same DNA profile.
(from http://chemserver.chem.orbelin.edu/RQT/PCRDNA/rflp.html)
