What is the main reason for purifying a restriction-cut insert?

Correct answer: To separate desired fragment from unwanted DNA

Direct answer: Option A, purify the desired insert to separate it from unwanted DNA and reaction components. After restriction digestion, the tube may contain the wanted fragment, unwanted vector or fragments, enzyme, salts, buffer, and sometimes DNA of incorrect size. Purification, often by gel extraction or a suitable cleanup method, selects the intended fragment and removes contaminants. This helps ligase join the correct molecules and improves ligation specificity, though yield and DNA damage must also be considered. Option A is correct. Option B is wrong because purification does not make the insert a protein. Option C is wrong because the purpose is to preserve and recover the desired insert, not destroy it. Option D is wrong because enzyme colouring has no role in cloning. Memory cue: purify the right band before joining it.