Which laboratory technique amplifies DNA in vitro using primers, DNA polymerase, and nucleotides?

• A. Southern blot
• B. Northern blot
• C. Polymerase Chain Reaction (PCR)
• D. Gel electrophoresis

Answer: (C)

PCR amplifies a specific piece of DNA in a test tube by cycling through heating and cooling steps that enable repeated rounds of DNA synthesis. It requires primers that flank the region to be copied, a DNA polymerase to build new strands, and nucleotides as building blocks. In each cycle, the DNA double helix denatures, the primers anneal to their complementary sequences, and the polymerase extends the primers to synthesize new DNA. After multiple cycles, the target sequence is amplified exponentially, producing millions of copies from a tiny starting amount. This differentiates PCR from methods like Southern or Northern blotting, which are used to detect DNA or RNA rather than amplify it, and from gel electrophoresis, which separates DNA fragments but does not increase their quantity.