Question

Which of the following is a characteristic feature of Bacterial Artificial Chromosome (BAC) vector?

• A. They can carry large DNA inserts.
• B. They use eukaryotic cells as hosts.
• C. They lack selectable markers.
• D. They do not replicate autonomously.

Hint:

Associate different cloning vectors with their insert size capacity.

\textbf{Plasmids:} Small inserts (\(<\) 15 kbp)
\textbf{Bacteriophages (e.g., Lambda):} Moderate inserts (\( \sim \) 25 kbp)
\textbf{Cosmids:} Larger inserts (\( \sim \) 45 kbp)
\textbf{BACs:} Very large inserts (150-350 kbp)
\textbf{YACs:} Extremely large inserts (\(>\) 1 Mbp)

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question focuses on identifying a key feature of Bacterial Artificial Chromosomes (BACs), which are cloning vectors used in molecular biology.
Step 2: Detailed Explanation:
Let's examine the characteristics of BAC vectors:

BACs are based on the F-plasmid (fertility plasmid) of {E. coli}.
A crucial feature is their capacity to accommodate and maintain large DNA inserts, typically ranging from 150 to 350 kilobase pairs (kbp). This makes them valuable for constructing genomic libraries and sequencing entire genomes.
They utilize bacterial cells (specifically {E. coli}) as hosts, as indicated by their name.
They contain essential vector components, including an origin of replication (oriS from the F-plasmid), enabling them to replicate autonomously within the host cell. The F-plasmid origin maintains a low copy number (1-2 copies per cell), enhancing the stability of large inserts.
They include selectable markers, such as antibiotic resistance genes (e.g., chloramphenicol resistance), allowing for the selection of cells that have successfully incorporated the vector.
Evaluating the options:

(A) They can carry large DNA inserts: This is a primary and defining characteristic of BACs.
(B) They use eukaryotic cells as hosts: This is incorrect. They use bacterial hosts. Yeast Artificial Chromosomes (YACs) use eukaryotic (yeast) hosts.
(C) They lack selectable markers: This is incorrect. Selectable markers are essential for cloning.
(D) They do not replicate autonomously: This is incorrect. They possess an origin of replication and replicate with the host cell's chromosome.
Step 3: Final Answer:
The most significant characteristic of a BAC vector is its ability to carry large DNA inserts.