What technique separates DNA fragments by size using an electric field?

• A. Pedigree
• B. Nondisjunction
• C. Restriction Enzyme
• D. Gel Electrophoresis

Answer: (D)

Size-based separation of DNA fragments is achieved by gel electrophoresis. DNA molecules are negatively charged, so when placed in a porous gel like agarose and an electric field is applied, they migrate toward the positive end. The gel’s pores create friction that slows movement, and smaller fragments slip through more easily and travel farther than larger ones in the same amount of time, producing a pattern that reflects size. After cutting DNA with restriction enzymes or amplifying it by PCR, you run the fragments on a gel to compare their lengths against a ladder. Other terms you might encounter describe related ideas—pedigrees map family inheritance, nondisjunction is when chromosomes fail to separate during cell division, and restriction enzymes cut DNA at specific sequences to create fragments—but the actual separation by size in an electric field is accomplished by gel electrophoresis.