Final answer:
In gel electrophoresis for small DNA fragments, use a gel with higher agarose or polyacrylamide concentration to finely resolve the fragments, and visualize with DNA-specific dye after separation.
Step-by-step explanation:
When performing gel electrophoresis with very small DNA fragments, it is crucial to use a gel with a higher concentration of agarose or polyacrylamide. This creates a finer matrix that can better resolve smaller DNA fragments. As the DNA is negatively charged at a neutral or basic pH, it will migrate towards the positive electrode when the electric current is applied; however, without an appropriately dense gel, those very small fragments can run through the gel too quickly and not separate sufficiently, resulting in a smear.
Therefore, the correct step to take is to prepare a gel with a suitable agarose concentration for the fragment sizes you are dealing with. After separation, the DNA is visualized with a DNA-specific dye like ethidium bromide, which binds to DNA and fluoresces under ultraviolet light, enabling the observation of the separated fragments.