Gel electrophoresis is used to

• A. Amplify DNA sequences.
• B. Measure RNA expression.
• C. Separate DNA fragments by size.
• D. Assemble DNA fragments into genomes.

Answer: (C)

Gel electrophoresis separates DNA fragments by size. In this method, DNA samples travel through an agarose gel under an electric field; the molecules are negatively charged, so they move toward the positive end. The gel’s matrix slows larger fragments more than smaller ones, causing fragments to spread out into bands that reflect their lengths. This allows you to estimate fragment sizes by comparing them to a DNA ladder with known sizes. This technique is commonly used to check PCR products or restriction enzyme digests and to profile DNA, but it doesn’t amplify DNA, measure RNA expression, or assemble genomes.