Q.36 Match the items in Group I with Group II
| Group I (Vectors) | Group II (Maximum DNA packaging) |
|---|---|
| P. λ phage | 1. 35–45 kb |
| Q. Bacterial Artificial Chromosomes (BACs) | 2. 100–300 kb |
| R. P1 derived Artificial Chromosomes (PACs) | 3. ≤ 300 kb |
| S. λ cosmid | 4. 5–25 kb |
Options:
(A) P-3, Q-4, R-1, S-2
(B) P-1, Q-3, R-2, S-4
(C) P-4, Q-3, R-2, S-1
(D) P-1, Q-2, R-3, S-4
Cloning Vectors Packaging Capacities: λ Phage, BACs, PACs, Cosmids
λ phage vectors package up to 20 kb inserts, while cosmids handle 35-45 kb via cos sites. BACs and PACs support massive 100-300 kb fragments for genomic libraries.
Correct Answer
Option (C) P-4, Q-3, R-2, S-1 is correct.
Matches: λ phage (5–25 kb), BACs (≤ 300 kb), PACs (100–300 kb), λ cosmid (35–45 kb). These align with standard insert capacities for stable cloning in E. coli.
Vector Capacities Explained
λ phage replacement vectors accept 5–25 kb inserts between stuffer fragments, limited by ~50 kb genome packaging.
BACs (F-factor based) stably carry ≤ 300 kb, ideal for large eukaryotic genomes.
PACs (P1 phage derived) package 100–300 kb with higher stability than BACs for complex libraries.
λ cosmids use cos sites for in vitro packaging of 35–45 kb, bridging plasmids and phages.
Option Breakdown
| Option | P (λ phage) | Q (BACs) | R (PACs) | S (λ cosmid) | Correct? | Reason |
|---|---|---|---|---|---|---|
| (A) | 3 (≤300 kb) | 4 (5–25 kb) | 1 (35–45 kb) | 2 (100–300 kb) | No | Mismatches all; λ phage too large |
| (B) | 1 (35–45 kb) | 3 (≤300 kb) | 2 (100–300 kb) | 4 (5–25 kb) | No | Cosmid capacity wrong; too low |
| (C) | 4 (5–25 kb) | 3 (≤300 kb) | 2 (100–300 kb) | 1 (35–45 kb) | Yes | Standard capacities match literature |
| (D) | 1 (35–45 kb) | 2 (100–300 kb) | 3 (≤300 kb) | 4 (5–25 kb) | No | λ phage/cosmid swapped; BACs too narrow |
Exam Applications
Use for genomic libraries: cosmids for 40 kb genes, BACs/PACs for chromosomes.
λ vectors suit small fragments; avoid >25 kb to prevent unstable packaging.
Key for biotech exams: memorize cosmid’s 37-52 kb packaging window.
