Now, let's begin by discussing what the ingredients are to this reaction. What is it that we need to actually carry out a successful polymerase chain reaction? So we have four important ingredients. 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.