Final answer:
DNA in gels is visualized with a fluorescent dye such as ethidium bromide, which binds to DNA and lights up under UV light.
Step-by-step explanation:
The DNA in gels can be visualized using a fluorescent dye, such as ethidium bromide, that binds to DNA. Known also as EtBr, this fluorescent compound intercalates with the nucleobases in DNA.
When gels containing DNA stained with EtBr are exposed to UV light, the nucleic acids “light up” in the gel, indicating where the DNA fragments are located. Gel electrophoresis is used to separate DNA fragments by size, as the negatively charged DNA molecules migrate from the negative towards the positive electrode.
Fragments of different lengths are then visualized as distinct bands on the gel.