PCR Schematic (IMAGE) University of California - Berkeley Caption Schematic showing the ultrafast photonic PCR using LED lights under a thin gold film to amplify genetic samples. The repeated heating and cooling process, called thermal cycling, is needed to separate the double-stranded DNA (1-Denaturation). Complementary bases from a primer then bind to the single strand (2-Annealing and extension), resulting in two copies of the gene. The process is repeated for at least 30 cycles. Credit Jun Ho Son, UC Berkeley Usage Restrictions Editorial use only. Must include credit. Commercial use prohibited. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.