Question

Among existing technologies , which of the following vector system would you prefer to use for generating a library for 140 kb eukaryotic genomic DNA fragments while giving due consideration to size as well as stability of insert

• A. Phage
• B. Cosmid
• C. Bacterial Artificial Chromosome (BAC)
• D. Phagemid

Hint:

Vector Insert Capacities:
Plasmids: $< 10\text{ kb}$.
$\lambda$ Phage: $15-25\text{ kb}$.
Cosmids: $35-45\text{ kb}$.
BACs: $100-300\text{ kb}$ (High stability).
YACs: $100-1000\text{ kb}$ (Prone to chimerism).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Cloning vector insert capacities and structural stability: Plasmids ($< 10 ext{ kb}$) $<$ $\lambda$ Phage ($< 25 ext{ kb}$) $<$ Cosmids ($35-45 ext{ kb}$) $<$ Fosmids ($40 ext{ kb}$) $<$ BACs ($100-300 ext{ kb}$) $<$ YACs ($> 1 ext{ Mb}$).

Step 2: Detailed Explanation:
Comparing vector cloning capacities for large genomic inserts:
1. Phage $\lambda$ Vectors: Maximum insert capacity $\approx 15 - 25\text{ kb}$.
2. Cosmid Vectors: Insert capacity limited to $\approx 35 - 45\text{ kb}$.
3. Bacterial Artificial Chromosomes (BACs): Based on the stable low-copy E. coli F-factor (fertility plasmid) replication origin (oriS, repE, parA, parB). BACs stably maintain large genomic inserts of 100 to 300 kb (ideal for 140 kb) with high structural stability and minimal chimerism/recombination.
4. Phagemids: Small plasmid/phage hybrids for single-stranded DNA ($< 10\text{ kb}$).

Step 3: Final Answer:
Therefore, the preferred vector is Bacterial Artificial Chromosome (BAC), matching option (C).