Why are restriction-cut DNA fragments shown in gel electrophoresis?

Correct answer: To compare fragment sizes

The governing concept is separation of charged DNA molecules by gel electrophoresis. DNA has a negatively charged phosphate backbone, so it migrates through an agarose gel toward the positive electrode when an electric field is applied. Smaller DNA fragments generally move through the gel matrix more easily and travel farther than larger fragments. After staining, the resulting bands reveal the number and approximate sizes of fragments produced by restriction digestion. Therefore option A is correct: gel electrophoresis allows fragment sizes to be compared, commonly with a DNA ladder as a reference. It does not measure water temperature, determine leaf age, or assess the taste of fat.