Question:

DNA strands on a gel stained with ethidium bromide when viewed under UV radiation, appear as :

Updated On: Nov 14, 2025

Yellow bands
Bright orange bands
Dark red bands
Bright blue bands

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The Correct Option is B

Solution and Explanation

To determine how DNA strands appear when stained with ethidium bromide and viewed under UV radiation, let's explore the chemistry and physics underlying this process:

Ethidium bromide is a fluorescent dye commonly used to stain DNA in agarose gel electrophoresis experiments. It intercalates between the bases of DNA strands.
The principle behind the staining lies in the fluorescence property of ethidium bromide. When exposed to UV light, ethidium bromide absorbs energy and emits it as visible light.
The emitted light from ethidium bromide-stained DNA is typically in the orange spectrum. This is due to the energy level transition that occurs within the ethidium bromide molecule, leading to bright orange fluorescence.

Therefore, when DNA stained with ethidium bromide is exposed to UV radiation on a gel, it appears as bright orange bands. The other options (yellow, dark red, and bright blue) do not accurately describe the fluorescence emitted by ethidium bromide under UV light.

Conclusion: The correct answer is Bright orange bands.

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DNA fingerprinting, also called DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing, in genetics, method of isolating and identifying variable elements within the base-pair sequence of DNA.

The procedure of DNA Fingerprinting:

The procedure for creating a DNA fingerprint consists of first obtaining a sample of cells, such as skin, hair, or blood cells, which contain DNA. The DNA is extracted from the cells and purified. In Jeffreys’s original approach, which was based on restriction fragment length polymorphism (RFLP) technology, the DNA was then cut at specific points along the strand with proteins known as restriction enzymes. The enzymes produced fragments of varying lengths that were sorted by placing them on a gel and then subjecting the gel to an electric current (electrophoresis): the shorter the fragment, the more quickly it moved toward the positive pole (anode). The sorted double-stranded DNA fragments were then subjected to a blotting technique in which they were split into single strands and transferred to a nylon sheet. The fragments underwent autoradiography in which they were exposed to DNA probes—pieces of synthetic DNA that were made radioactive and that bound to the minisatellites. A piece of X-ray film was then exposed to the fragments, and a dark mark was produced at any point where a radioactive probe had become attached. The resultant pattern of marks could then be analyzed.