What should be done to preserve high molecular weight DNA?

Correct answer: Pipette gently and mix carefully

High molecular weight DNA consists of long strands that can break into smaller fragments during vigorous vortexing, harsh pipetting, or repeated freeze-thaw cycles. Gentle pipetting and careful mixing minimise DNA shearing, so this is the correct practice. Exam tip: For intact long DNA, remember “gentle handling; avoid vigorous mixing.”