Why are multiple cycles used in PCR (Polymerase Chain Reaction)?

Multiple cycles in the Polymerase Chain Reaction (PCR) are utilized to exponentially amplify specific segments of DNA. Each cycle consists of repeated processes of denaturation, annealing, and extension, which lead to the creation of new DNA strands based on the target sequence. When these cycles are repeated, the amount of target DNA doubles with each cycle, resulting in millions of copies after a sufficient number of cycles. This amplification is crucial for various applications, such as genetic analysis, forensics, and medical diagnostics, where large quantities of DNA are needed from a relatively small starting sample.

The other options, while they touch on different aspects of molecular biology, do not capture the primary function of multiple cycles in PCR. Decreasing sample size is not a goal of PCR; in fact, the purpose is to increase the total amount of DNA. Allowing for DNA mutation is more relevant to other experimental designs, such as mutagenesis, rather than what PCR is designed to do. Slowing down the reaction would be contrary to the goal of PCR, which is to quickly replicate DNA for testing and analysis. Thus, the correct answer highlights the fundamental purpose of the amplification process inherent in PCR.