The problem with RFLP analysis is that it requires a relatively large amount of DNA, which in turn requires a relatively large
amount of sample. This hinders its usefulness in the field of forensics. By contrast, the Polymerase Chain Reaction allows us to
develop a DNA profile from as little DNA as might be deposited by licking an envelope! PCR can do this because instead of
cutting out the target STR sequences from the rest of the genome, it amplifies the sequences by replicating them over and over.
DNA is replicated by the naturally occurring enzyme DNA polymerase. In nature, the two strands of the DNA molecule are
replicated individually and in their entirety -- there is never replication of just one section of DNA. To force the replication of
specific sequences of the genome, scientists have developed special DNA primers that recognize and stick to
specific sequences, and enable DNA polymerase to replicate only those sequences enclosed by the primers.
Since we know the desired STR sequences, and we know some of the bases before and after the STR, we can
construct primers that will attach themselves on either side and allow replication of the sequence in-between.