Read the Passage carefully and answer the questions.

The DNA fragments can be separated by a technique known as gel electrophoresis. Since DNA fragments are negatively charged molecules, they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation. The repeated amplification of DNA is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus). After completion of the biosynthetic stage, the product has to be subjected through a series of processes before it is ready for marketing as a finished product. The downstream processing and quality control testing vary from product to product. The convention for naming restriction enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated.

In agarose gel electrophoresis, the DNA fragments can be visualised only after staining the DNA with a compound known as -

Ethidium bromide

The correct answer is Option (3) → Ethidium bromide 

The process of cutting DNA using restriction endonucleases results in the formation of DNA fragments. These fragments can be separated using a technique called gel electrophoresis. Since DNA fragments are negatively charged molecules, they can be separated by applying an electric field, causing them to move towards the anode through a medium or matrix. Agarose, a natural polymer extracted from seaweeds, is commonly used as the matrix. The DNA fragments separate based on their size due to the sieving effect provided by the agarose gel. Smaller fragments move farther compared to larger fragments.

The separated DNA fragments can be visualized only after staining the DNA with a compound called ethidium bromide, followed by exposure to UV radiation. Without staining, the pure DNA fragments cannot be seen in visible light. After staining, we can observe bright orange-colored bands of DNA in an ethidium bromide stained gel exposed to UV light.

Once the DNA fragments are separated, they can be cut out from the agarose gel and extracted from the gel piece. This step is known as elution. The purified DNA fragments obtained through elution are then used in constructing recombinant DNA by joining them with cloning vectors.