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 asks for a key characteristic of a Bacterial Artificial Chromosome (BAC) vector. BACs are cloning vectors used in molecular biology.
Step 2: Detailed Explanation:
Let's analyze the features of BAC vectors:

BACs are based on the F-plasmid (fertility plasmid) of {E. coli}.
Their most important feature is their ability to accept and maintain very large DNA inserts, typically ranging from 150 to 350 kilobase pairs (kbp). This makes them invaluable for constructing genomic libraries and for sequencing entire genomes.
They use bacterial cells (specifically {E. coli}) as hosts, as indicated by the name "Bacterial" Artificial Chromosome.
They contain essential vector components, including an origin of replication (oriS from the F-plasmid) that allows them to replicate autonomously in the host cell. The F-plasmid origin maintains a very low copy number (1-2 copies per cell), which contributes to the stability of large inserts.
They possess selectable markers, such as an antibiotic resistance gene (e.g., chloramphenicol resistance), to allow for the selection of host cells that have successfully taken up the vector.
Evaluating the options:

(A) They can carry large DNA inserts: This is the 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. They must have selectable markers for cloning to be feasible.
(D) They do not replicate autonomously: This is incorrect. They have an origin of replication and replicate along with the host cell's chromosome.
Step 3: Final Answer:
The most significant characteristic feature of a BAC vector is its capacity to carry large DNA inserts.