What is the procedure used to separate and analyze DNA fragments by applying an electric field to a gel?

• A. DNA polymerase
• B. Gel electrophoresis
• C. Ligase
• D. Okazaki fragments

Answer: (B)

Separating and analyzing DNA fragments by applying an electric field to a gel is gel electrophoresis. In this method, DNA carries a negative charge and moves toward the positive electrode when the electric field is applied. The gel matrix acts like a sieve: smaller fragments navigate the pores more easily and migrate faster, while larger fragments lag behind, producing a size-based pattern of bands. The gel’s composition and the voltage used affect how well fragments separate, and a DNA ladder or size marker helps estimate fragment sizes. After running the gel, DNA bands are visualized by staining with a DNA-binding dye and viewing under UV or blue-light illumination. This technique is commonly used to check fragment sizes after restriction enzyme digestion, verify PCR products, or analyze DNA samples. The other options describe enzymes or concepts involved in DNA synthesis or replication, not a method for separating DNA by size, so they don’t fit the procedure.