How can gel electrophoresis be used to analyze DNA fragments?

• A. It separates DNA fragments by charge in an electric field.
• B. It measures DNA sequence directly.
• C. It separates DNA fragments by size in an electric field.
• D. It quantifies DNA concentration.

Answer: (C)

Gel electrophoresis analyzes DNA fragments by size as they move through a gel matrix under an electric field. DNA carries negative charges due to its phosphate backbone, so it migrates toward the positive electrode when voltage is applied. The gel acts like a sieve: smaller fragments slip through the pores more easily and travel farther in a given time, while larger fragments move more slowly. By running a DNA ladder with known fragment sizes alongside the samples, you can estimate the lengths of the fragments in your lanes. This size-based separation is why gel electrophoresis is used to analyze DNA fragments.