A much more effective and a much more efficient and accurate method is the polymerase chain reaction, or PCR. Now, the polymerase chain reaction allows us to amplify a certain gene, a certain sequence of DNA, very quickly. So we can produce millions or even billions of copies of a single segment of DNA that we're actually interested in. 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.