Final answer:
Ethidium bromide (EtBr) is the dye commonly used to visualize nucleic acids in agarose gel electrophoresis because of its fluorescent properties that light up nucleic acids under UV light.
Step-by-step explanation:
A dye often used for its ease and sensitivity to visualize nucleic acids after agarose gel electrophoresis is ethidium bromide (EtBr). This dye is popular because it is fluorescent and intercalates with DNA bases, which allows it to emit light when exposed to UV light during gel examination.
When a gel is stained with ethidium bromide, and then photographed under ultraviolet light, the nucleic acids within the gel "light up", providing a clear indication of the DNA fragments' presence and size. This process is essential in molecular biology to assess the success of DNA amplification and to estimate the size of fragments. Alongside molecular weight ladders, it helps scientists to determine the approximate size of the nucleic acid fragments separated by gel electrophoresis.