Basically these sequences found on both sides of that gene of interest. So the flanking sequence is a segment of DNA that we do not want to replicate, but that we know the sequence of nucleotides because we have to know what the sequence within these sections here, because we're going to build the DNA primers that can essentially hybridize with those flanking regions. Because the DNA polymerase that is used in the polymerase chain reaction needs the primus to actually synthesize the DNA molecule. So PCR requires that we know the flanking sequence of nucleotides surrounding that target DNA segment. We need this sequence to produce DNA primers needed for replication. Now let's actually take a look at the process of polymerase chain reaction.