What technique is used to amplify DNA by repeated cycles of heating and cooling?

• A. PCR
• B. RAPD
• C. Sanger Sequencing
• D. RFLP

Answer: (A)

Amplification of DNA through repeated cycles of heating and cooling is PCR, which stands for polymerase chain reaction. In PCR you repeatedly denature the double-stranded DNA with heat, allow short primers to bind to the target region during a cooling step, and then extend new DNA strands from those primers with a DNA polymerase. Doing this over many cycles multiplies the target DNA exponentially, so a tiny amount of starting material becomes millions of copies.

This requires a thermostable DNA polymerase so the enzyme can survive the high temperatures used to separate the strands. That combination of cycles and primers that specify the region to copy is what makes PCR the go-to method for DNA amplification.

Other techniques don’t fit this description as their primary purpose or mechanism isn’t about cycling to amplify a specific DNA fragment. Sanger sequencing reads the sequence of DNA, not its amplification; RFLP analyzes fragment sizes after restriction digestion rather than expanding copies by cycles; RAPD is a PCR-based fingerprinting approach using random primers, but the defining feature in the question is the general, targeted amplification by repeating heating and cooling cycles, which points to PCR.