What practice is good to protect large DNA fragments?

Correct answer: Gentle handling and low UV exposure

The direct answer is A: use gentle handling and low UV exposure. Large DNA fragments are long molecules and can be broken by strong physical forces. Harsh vortexing, repeated forceful pipetting, and rough transfers may shear them into smaller pieces. UV light used to see DNA bands can also damage DNA, so exposure should be kept as short and low as practical. Option A is correct because careful handling and reduced UV help preserve fragment length and recovery. Option B is wrong because harsh vortexing increases mechanical shearing. Option C is wrong because long UV exposure increases DNA damage rather than protecting the sample. Option D is wrong because unlabeled tubes do not protect DNA and can cause sample mix-ups, although correct labeling is also good laboratory practice. Work gently, use suitable tools, and minimize unnecessary illumination. Memory cue: big DNA needs “soft hands and short UV.”