Read the passage and answer the following question :
The cutting of DNA by restriction endonucleases results in the fragments of DNA. These 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 commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate according to their size through sieving effect provided by the agarose gel. Hence, the smaller fragments move farther in the agarose gel. The separated DNA fragments can be visualised only after staining the DNA with ethidium bromide followed by exposure to UV radiation. Bright orange coloured bands of DNA can be observed. The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution. The DNA fragments purified in this way are used in constructing recombinant DNA by joining them with cloning vectors.
The fragments of DNA separate on agarose gel, based on the____________.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Size of fragments
Option (1) Size of fragments — Correct. The agarose gel works like a sieve: as the passage says, the fragments separate according to their size, and smaller fragments move farther.
Option (2) Charge of each fragment — Incorrect. All DNA fragments carry a negative charge; the charge makes them move to the anode, but it does not separate them from one another.
Option (3) Colour of fragment — Incorrect. DNA is colourless; it is seen only after staining with ethidium bromide.
Option (4) Type of DNA — Incorrect. The fragments come from the same DNA, cut by restriction enzymes; they differ only in length.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.