Gel Electrophoresis
Read the following passage carefully and answer the questions given below:
As a result of cutting DNA by restriction endonucleases, DNA becomes fragmented. These fragments can be separated by gel electrophoresis. Since DNA fragments are negatively charged, they are made to move towards the anode under an electric field and are separated according to their size. The matrix agarose, which is commonly used nowadays, is a natural polymer extracted from seaweeds. DNA fragments move through the sieving effect of the agarose gel and get separated according to their size. Therefore, the smaller the fragment size, the farther they move. After staining the separated DNA fragments with a compound called ethidium bromide, they can be seen as bright orange coloured bands when exposed to UV radiation. The separated DNA fragments are cut out from the agarose gel and extracted from the gel pieces. This process is called elution. The DNA purified in this way is joined to cloning vectors for the construction of recombinant DNA.
When ethidium bromide-stained gel is exposed to UV light, DNA bands of __________ colour can be seen.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Orange
The separated DNA fragments are made visible by staining the gel with ethidium bromide and then exposing it to UV radiation. The DNA fragments then appear as bright orange coloured bands.
(1) Green — Incorrect. Ethidium bromide-stained DNA does not glow green.
(2) Purple — Incorrect. The bands are not purple.
(3) Yellow — Incorrect. The bands are not yellow.
(4) Orange — Correct. The DNA shows as bright orange bands under UV light.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.