Number one, we actually need that segment of DNA, the double stranded DNA that we want to amplify, that we want to replicate. So we have to begin with a certain target DNA molecule that contains that sequence, that gene that we want to amplify. Number two, we need a pair of DNA primer. So what is a DNA primer? Well, remember, a DNA primer is a relatively short sequence of DNA, so ranges from about 20 to 30 nucleotides. And what this is used for is to initiate the process of DNA synthesis, DNA replication.