So what do we mean by a flanking sequence? So let's take a look at the following double transit DNA molecule. Let's suppose you're given this molecule and this is the gene that we actually want to amplify. So it begins here and ends here. Now we don't know what the sequence of nucleotides in this target sequences, the target sequence of the sequence we want to amplify, but we do know where that DNA segment is found. We do know what the flanking sequences, the flanking sequence are.