Which technology creates billions of copies of a DNA segment for analysis?

• A. Cloning
• B. DNA microarray
• C. Sequencing
• D. Polymerase chain reaction

Answer: (D)

DNA amplification of a specific DNA fragment is achieved by polymerase chain reaction. This method uses primers that flank the target region and a heat-stable DNA polymerase to synthesize new DNA strands. By cycling through heating and cooling steps—denaturation to separate strands, annealing of primers, and extension to build new copies—the amount of the target DNA doubles with each cycle. After many cycles, a tiny starting amount can yield billions of copies, making the segment easy to analyze.

This is the best choice because it is specifically designed to massively and rapidly amplify a defined DNA region. Other techniques don’t inherently produce billions of copies of a targeted segment: cloning involves replicating DNA in cells over longer times; DNA microarrays are for detecting the presence or activity of many sequences rather than amplifying them; sequencing reveals order of bases but isn’t, on its own, a massive amplification method.