Which of the following statements are correct with respect to DNA separation, isolation and visualization ?

A. The cutting of DNA is done by molecular scissors.
B. The DNAfragments separate according to their size in an agarose gel, upon electrophoresis.
C. The separated DNA fragments can be seen without staining when exposed to UV light.
D. The separated DNA fragments, when stained with ethidium bromide, can be seen in visible light.

Choose the correct answer from the options given below :

**Statement A – “The cutting of DNA is done by molecular scissors.”**
Restriction enzymes are often described as “molecular scissors” because they recognize specific DNA sequences and cleave the phosphodiester backbone at or near those sites. This analogy is widely used in molecular biology textbooks and therefore the statement is true.

**Statement B – “The DNA fragments separate according to their size in an agarose gel, upon electrophoresis.”**
When an electric field is applied across an agarose gel, negatively‑charged DNA molecules migrate toward the anode. The porous matrix of the gel impedes larger fragments more than smaller ones, so fragments are sorted by size. This is the fundamental principle of agarose‑gel electrophoresis, making the statement true.

**Statement C – “The separated DNA fragments can be seen without staining when exposed to UV light.”**
DNA itself does not absorb UV light in a way that produces visible fluorescence. To visualize the bands, the gel must be stained with a fluorescent dye (e.g., ethidium bromide, SYBR Gold). Without such a stain, the fragments remain invisible under UV illumination. Hence, the statement is false.

**Statement D – “The separated DNA fragments, when stained with ethidium bromide, can be seen in visible light.”**
Ethidium bromide intercalates between base pairs and, when illuminated with UV light, emits orange‑red fluorescence. This fluorescence is not visible under ordinary white‑light illumination; it requires UV excitation. Therefore, the statement is false.

Combining the truth values, the only correct pair of statements is **A and B only**.