DNA Fingerprinting

DNA fingerprinting is a relatively new study, beginning in the 1980s, and revolutionizing forensic investigations. DNA fingerprinting refers to the identification of an individual based on the unique patterns found in their DNA samples. This was extremely new at the time and made identifying suspects more reliable than just going off of given alibis. DNA fingerprinting has caused some controversy in the effectiveness of the process, but since its discovery, many uses have been found such as, paternal identification, criminal cases in finding the suspect, and identification of the perpetrator in rape cases.

Restriction Fragment Length Polymorphism (RFLP) is a method used for DNA fingerprinting by means of gel electrophoresis. During gel electrophoresis,

Radioactive DNA probes that have been designed to attach themselves to particular DNA fragments are added. The locations in the gel of these fragments are indicated as bands on X-ray film, called an autoradiogram and allow technicians to measure the distances travelled. These distances converted to molecular weights or "band weights" (in kilobases (kb): thousands of Watson-Crick base pairs) (p. 176).

The lengths of the segments are compared to the targeted DNA sequence. In forensic uses, the targeted DNA sample could come from blood, hair, or skin cells left behind at the crime scene. If there is a match in the lengths between the suspect's DNA and the sample found at the crime scene, then further steps are taken. Scientists will calculate a "match percentage," which is the proportion that the two DNA samples are a match. If the suspect has even one band weight that does not match that of the sample from the crime scene, then they can be eliminated for they are not the same person.

RFLP analysis refers to the examination of the autoradiogram to determine the specific pattern of the VNTR (variable number tandem repeats), which are repetitive sequences of base pairs found in the non-coding regions of our DNA. That pattern of VNTR is your DNA

"A DNA polymerase, an enzyme involved in making new copies of DNA, is used to copy a small segment of DNA over and over again... Millions of exact copies are produced" (A. Silverstein, V. Silverstein, & L. Silverstein Nunn, 2001). This allows investigators to only need a small sample of DNA from the crime scene to prevent any further tampering. Since RFLP requires quite a bit of DNA, this process is very helpful. By amplifying small portions of an individual's DNA, technicians can run the DNA through the gel as many times as needed to minimize errors in RFLP or AmpFLP