After electrophoresis of a restriction digest, a researcher sees several DNA bands at different distances from the loading well. What determines how far a fragment traveled?

Core Concept

Every nucleotide carries one phosphate, giving all fragments nearly identical charge per unit mass. The electric field therefore pulls them toward the positive electrode with comparable force. The agarose matrix acts as a molecular sieve, and shorter fragments weave through the pores faster than long ones. Migration distance thus reports fragment size against a reference ladder.