What is PCR and why is it useful?

• A. PCR amplifies a targeted DNA segment for analysis, cloning, or diagnostics.
• B. It sequences entire genomes to compare species.
• C. It reduces DNA to a single strand for editing.
• D. It mutates DNA to study changes.

Answer: (A)

PCR is a method that copies a specific piece of DNA many times, so a tiny sample can become enough material to study. It uses short pieces of DNA called primers that flank the region you’re interested in, a heat-stable DNA polymerase to build new DNA, and cycles of heating and cooling that unzip the DNA, let the primers attach, and extend the new strands. Because the process repeats, the target DNA segment is amplified exponentially, giving millions of copies.

This amplification is incredibly useful because it makes analysis possible on samples that would be too small to work with directly. It lets scientists sequence or characterize the fragment, clone it into a plasmid for further study, or run diagnostic tests to detect pathogens or specific genetic variants.

Other options describe actions that aren’t the core use of PCR. Sequencing an entire genome is done with dedicated sequencing technologies that read many fragments, not the main function of PCR. Reducing DNA to a single strand or mutating DNA aren’t the primary purposes of PCR, though certain specialized techniques can involve strand separation or introduce changes, they’re not what PCR is mainly used for.