The restriction fragment length polymorphism or RFLP (sometimes called DNA fingerprinting or profiling) is considered to be the more accurate of the two. This test examined sequences of base pairs in a section of a DNA strand with a high probability of being entirely unique to the donor. When a match is found, there is no question that the donor was at the scene of the crime. It’s very conclusive and finalizing. Unfortunately, the RFLP requires many sample cells from the crime scene like several strands of hair or large splatters of blood. The cells have to be “fresh”, too--that is, undamaged and recently dead. The test takes anywhere from 3 weeks to three months to complete, also.

Electrophoresis Analogy

Electrophoresis gel
By permission University of Illinois

Although the PCR test, or polymerase chain reaction test, isn’t quite as accurate, it takes much less time to complete--a week at most. The test can be performed with minute crime scene samples, to, which helps investigators who have little physical evidence. The DNA doesn’t have to be recently collected, either; the PCR test can still be performed even years after--decades after--the fact, and still be just as accurate. This is because the PCT method involves copying the available DNA and analyzing only one specific gene, oftentimes the gene called HLA DQ alpha. Geneticists look for certain types of the gene (alleles) to determine matches. If no match is found, the donor was not at the crime scene. Matches are not conclusive, though, because many people may have--and are more than likely to have--the same alleles as the donor. Still, juries have convicted suspects based on PCR test results.

PCR Analogy