In the annealing stage, the primers, called forward and reverse primers, attach to the complementary strand of the DNA to initiate the replication process. They are heat-resistant, short pieces of the DNA that are designed to be complementary to the sequence of the target DNA strand (National Library of Medicine [NIH], 2017). These primers indicate the start and the end of replication and are necessary for the polymerase enzyme to build the complementary DNA in the next stage. Lastly, the annealing stage works best in around 50-68°C . More specifically, the optimum temperature is around 5°C lower than the melting temperature of the primers because too low temperatures may cause the primers to bind nonspecifically to the template.