Polymerase chain reaction (PCR)

In the polymerase chain reaction (PCR), unamplified target DNA (red and black strands at top) is separated into two single strands by heating. Next, primers (green and blue arrows) anneal to the opposite DNA strands of the desired target sequence. The complementary strand is then synthesized (longer blue and green arrows). Subsequent cycles of strand separation (denaturing), primer hybridization (annealing), and strand synthesis (extension) ensure exponential amplification of the target sequence by using the amplified sequences of the previous cycle as a new template (as shown in the Second PCR cycle). The target PCR product, which consists of approximately 10(6) copies after 30 cycles, is shown at the bottom of the figure.