​Which one of the following combinations of enzymes used for cloning a linear insert fragment into a digested plasmid vector would have the least probability of generating self-ligated vectors in a cloning experiment following complete digestion of all vector molecules and no further enzymatic treatment of the vector?​

Correct option is C

Explanation-

To avoid self-ligation of the vector - Use two different restriction enzymes that generate non-compatible (non-cohesive) ends, i.e., non-palindromic sticky ends. This ensures that vector ends cannot ligate to themselves, but can ligate to the insert which has matching ends.
Analysis of the Options:
Option a: SmaI – SmaI
Produces blunt ends.
Blunt ends can ligate to each other easily (vector self-ligation is likely).
High probability of self-ligation.
Option b: SmaI – HincII
Both produce blunt ends.
Again, high chance of vector re-ligation.
Still high probability of self-ligation.
Option c: HindIII – XhoI
Both produce sticky ends, but with non-compatible overhangs:
HindIII: A↓AGCTT
XhoI: C↓TCGAG
These cannot ligate to each other, thus preventing self-ligation of the vector.
Option d: EcoRI – EcoRI
Both ends are identical sticky ends, so vector ends can ligate back together.
High probability of self-ligation.

Final Answer: Option c is correct