Which technique is used to separate DNA fragments based on size?

The technique that separates DNA fragments based on size is gel electrophoresis. This method involves the use of a gel matrix, usually made of agarose or polyacrylamide, which creates a porous medium through which DNA fragments can migrate. When an electric current is applied, negatively charged DNA fragments move towards the positive electrode. Smaller fragments travel faster and farther through the gel compared to larger ones because they encounter less resistance from the gel matrix. Consequently, after the electrophoresis run is complete, the DNA fragments can be visualized, and their sizes can be determined by comparing them to a standard ladder of known fragment sizes.

Other techniques listed have different purposes, such as polymerase chain reaction, which is used for amplifying DNA; enzyme-linked immunosorbent assay, which is a method for detecting proteins; and Western blotting, which is used to detect specific proteins in a sample. None of these alternatives are designed specifically for separating DNA fragments based on size, which solidifies gel electrophoresis as the appropriate choice.