Do longer or shorter nucleotides travel farther in the gel?

• A. Longer nucleotides travel farther.
• B. DNA fragments travel the same distance regardless of length.
• C. Shorter nucleotides travel farther.
• D. The travel distance depends on base composition rather than length.

Answer: (C)

Mobility in an agarose gel is determined by fragment size: shorter DNA fragments travel farther under the same electric field. The gel’s porous matrix creates resistance, and smaller pieces weave through the pores with less friction, so they migrate faster and cover more distance toward the positive electrode. Longer DNA fragments encounter more hindrance and move more slowly, ending up closer to where they started. The distance isn’t mainly about base composition under these conditions, so fragments don’t end up at the same spot regardless of length.