How does double digest improve a restriction map?

Correct answer: By indicating relative positions of two enzyme sites

The direct answer is A: a double digest indicates the relative positions of sites for two restriction enzymes. In a double digest, both enzymes act on the same DNA molecule. Their combined cuts produce fragments whose sizes depend on the distances between the recognition sites. By comparing these fragment sizes with single-digest results and the total DNA length, one can infer the order and relative spacing of the sites and draw a clearer restriction map. Option A is correct because the fragment pattern contains positional information. Option B is wrong because restriction enzymes cut DNA; they do not convert DNA into protein. Option C is wrong because a double digest does not stop electrophoresis or the gel itself. Option D is wrong because simply heating the sample is not the defining purpose of a double digest and may damage the reaction. Always interpret a double digest together with controls and expected fragment sizes. Memory cue: two enzymes, combined cuts, clearer positions.