GATE BT 2023 • Q45
MSQ • 2 Marks
Section 3: Genetics, Cellular and Molecular Biology
CRISPR-Cas9 gene editing
Subtopic: Fundamentals of CRISPR-Cas9 gene editing
Question Statement:
Which of the following vector(s) is(are) used to clone a DNA fragment of size
220 kb?
Options:
-
(A) Bacterial artificial chromosome
-
(B) Yeast artificial chromosome
-
(C) Cosmids
-
(D) pUC19 plasmid
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2023 Q.45)**
**1. Governing Concept**:
- **Topic**: Recombinant DNA Technology & Cloning Vector Capacities
- Cloning vectors have distinct maximum insert size capacities:
- Standard plasmids: up to **~10–15 kb**.
- Bacteriophage $\lambda$ replacement vectors: **~9–23 kb**.
- Cosmids: **~30–45 kb**.
- P1-derived artificial chromosomes (PACs): **~100–300 kb**.
- **Bacterial Artificial Chromosomes (BACs)**: **~100–350 kb** (based on *E. coli* F-plasmid replicon).
- **Yeast Artificial Chromosomes (YACs)**: **~100–2000 kb** (contain yeast centromere, telomeres, and ARS).
- To clone a **220 kb** DNA fragment, only high-capacity artificial chromosome vectors (BACs or YACs) can accommodate the insert.
**2. Option Analysis**:
- **Option (A) [Bacterial Artificial Chromosome (BAC)] is CORRECT**: Capable of stably carrying inserts ranging from 100 to 350 kb.
- **Option (B) [Yeast Artificial Chromosome (YAC)] is CORRECT**: Accommodates very large eukaryotic genomic DNA fragments from 100 kb up to 2 Mb.
- **Option (C) [Cosmid] is INCORRECT**: Upper cloning limit is strictly ~45 kb due to lambda bacteriophage head packaging limits.
- **Option (D) [Bacteriophage lambda vector] is INCORRECT**: Upper cloning limit is ~20–25 kb.
**3. Final Answer**:
- **Correct Options**: **A, B**
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