A dye needs to be added to the gel electrophoresis
Explanation:
Ethidium bromide (EtBr) is a reagent that adheres to DNA and fluoresces under ultraviolet (UV) light. Due to this feature, EtBr is widely used to dye DNA strands in molecular biology techniques such as agarose gel electrophoresis. The most common dyes for visualizing and staining nucleic acids during gel electrophoresis include EtBr, SYBR gold, Eva green and SYBR safe. If EtBr (or any other staining agent) was not added to the electrophoresis gel and/or running buffer, the gel will be dark under UV light (even the ladder lane will look empty) because DNA has not been stained.