The polymerase chain reaction is used to

• A. Amplify a specific DNA sequence to produce many copies
• B. Sequence an entire genome
• C. Digest DNA into smaller fragments
• D. Convert RNA into DNA

Answer: (A)

PCR is used to amplify a specific DNA sequence, producing many copies from a small starting amount. It does this through repeated cycles of denaturation, primer binding, and extension with a DNA polymerase, with the primers defining exactly which DNA segment is copied. Because each cycle doubles the amount of the target sequence, the region of interest grows exponentially and becomes available for analysis, cloning, or sequencing. This is different from sequencing an entire genome, which reads the order of bases across all of the DNA, from digesting DNA into smaller fragments with restriction enzymes, or from converting RNA into DNA (which is done by reverse transcription before a PCR step in RT-PCR).