​Given below are recognition sites of some restriction enzymes with the sites of restriction marked with a ‘^’ symbol.​

​EcoRV : GAT^ATC    Aval : C^YCGRG

HindIII : A^AGCTT    Sall : G^TCGAC

SmaI : CCC^GGG    XbaI : T^CTAGA

Which one of the following options represents all enzyme-treated vector (V) and insert (I) fragment combinations that would generate compatible ends for ligation without any other intermediate enzymatic treatment?​

Correct option is D

EXPLANATION-

EcoRV cuts at: GAT^ATC → blunt ends (cuts straight through).  SmaI cuts at: CCC^GGG → blunt ends.

Blunt ends can ligate directly with any other blunt ends, regardless of sequence, so EcoRV and SmaI ends are compatible.

AvaI cuts at: C^YCGRG (Y = C or T; R = A or G). The site is C Y C G R G, and the cut is after the first C.  SalI cuts at: G^TCGAC

Both produce compatible sticky ends due to their sequences (the degenerate bases Y and R allow complementarity).

​Therefore, Option (d)  is correct because it includes two pairs of compatible ends for ligation without any intermediate enzymatic treatment.

EcoRV (blunt) and SmaI (blunt) ends compatible.
AvaI and SalI sticky ends compatible.