What procedure is used to separate and analyze DNA fragments by applying an electrical voltage to a gel?

The procedure used to separate and analyze DNA fragments by applying an electrical voltage to a gel is electrophoresis. This technique involves placing a mixture of DNA fragments into a gel matrix and then applying an electric current. Because DNA fragments are negatively charged due to their phosphate backbone, they migrate towards the positive electrode when the voltage is applied. The gel acts as a molecular sieve, allowing smaller fragments to move faster and further than larger ones. As a result, DNA fragments are separated based on their size, which can then be visualized, allowing researchers to analyze the fragment lengths and compare them to known standards.

While other methods listed have their own specific purposes—such as polymerase chain reaction for amplifying DNA, gel filtration for separating molecules based on their size in a liquid medium, and Western blotting for detecting specific proteins—the process that specifically uses an electric field to resolve DNA fragments is electrophoresis. This distinctive aspect makes electrophoresis the correct answer for the separation and analysis of DNA fragments.