Which of the following statements is correct regarding visualizing DNA molecules separated by agarose gel electrophoresis?

Ethidium bromide stained DNA can be seen under exposure to UV light.

The correct answer is Option (4) - Ethidium bromide stained DNA can be seen under exposure to UV light.

After agarose gel electrophoresis, the separated DNA fragments are not visible to the naked eye. To visualize the DNA fragments, they need to be stained with a compound called ethidium bromide, which binds to the DNA molecules and fluoresces under UV light. Once the DNA is stained with ethidium bromide, it appears as bright orange-colored bands in the gel when exposed to UV light .

The next step in the process is to cut out the desired DNA bands from the agarose gel. This process is known as elution. The gel pieces containing the DNA bands of interest are carefully excised from the gel, and the DNA is then extracted from these gel pieces.

The purified DNA fragments obtained through elution can be used in constructing recombinant DNA. This involves joining the purified DNA fragments with cloning vectors, such as plasmids or bacteriophages, to create recombinant DNA molecules. These recombinant DNA molecules can then be introduced into host cells to produce the desired protein or to study specific genes.