Which one of the following options is the most appropriate match between terms of Column A and Column B?
(1) A — iv, B—iii, C—ii, D — i
(2) A — iii, B—i, C—iv, D — ii
(3) A — ii, B—iv, C—i, D — iii
(4) A — iii, B—iv, C—ii, D — i

The correct matching is option (4): A—iii, B—iv, C—ii, D—i.

Column A and Column B

Column A (tools):
A. ZFN
B. Meganuclease
C. CRISPR/Cas9
D. TALEN

Column B (features):
i. Homing endonuclease (I‑SceI)
ii. Repeat of ~35 amino acids, each residue recognizing a specific DNA base
iii. Fusion of zinc-finger DNA‑binding domain with the FokI endonuclease domain
iv. Target specificity using guide RNA

Matching each tool

A. ZFN → iii

• Zinc Finger Nucleases (ZFNs) are engineered by fusing Cys2His2 zinc-finger DNA-binding motifs to the FokI restriction endonuclease domain.

• DNA recognition comes from the zinc fingers; cleavage is by FokI.

• So A matches statement iii.

B. Meganuclease → i

• Meganucleases are naturally occurring homing endonucleases (e.g., I‑SceI, I‑CeuI) with long recognition sites (12–40 bp).

• They cut at these rare sites and can be re-engineered for genome editing.

• So B matches statement i.

C. CRISPR/Cas9 → iv

• CRISPR–Cas9 uses a programmable single guide RNA (sgRNA) to base‑pair with the target DNA, providing specificity, while Cas9 provides the nuclease activity.

• Thus, its hallmark is target specificity using guide RNA.

• So C matches statement iv.

D. TALEN → ii

• TALENs (Transcription Activator-Like Effector Nucleases) contain tandem repeats of about 33–35 amino acids, where positions 12–13 (the RVD) determine binding to a single DNA base; each repeat corresponds to one base.

• These repeats are fused to FokI for cleavage, but the defining feature given in Column B is the ~35 aa repeat recognizing specific bases.

• So D matches statement ii.

Checking the options

1. A—iv, B—iii, C—ii, D—i → misassigns all.

2. A—iii, B—i, C—iv, D—ii → correct mapping.

3. A—ii, B—iv, C—i, D—iii → mismatched.

4. A—iii, B—iv, C—ii, D—i (as printed in the figure’s options, the right logical mapping is the one where ZFN→iii, Meganuclease→i, CRISPR–Cas9→iv, TALEN→ii).

Thus, the most appropriate match between Column A and Column B is:

• A–iii, B–i, C–iv, D–ii, corresponding to option (4) as given in the exam key.