To that end, the “ingredients” are the target DNA, nucleotides, DNA primer, and DNA polymerase (specifically Taq polymerase, which can survive the high temperatures required in PCR).
PCR is used to amplify DNA in its entirety. While fragments of varying lengths may be produced by accident (e.g., the DNA polymerase might fall off), the goal is to duplicate the entire DNA sequence. To that end, the “ingredients” are the target DNA, nucleotides, DNA primer, and DNA polymerase (specifically Taq polymerase, which can survive the high temperatures required in PCR).