Question

Which of the following are the properties of a good cloning vector
(A). Ideally should be less than 10 kb
(B). Isolation and purification should be easy
(C). Should contain a unique target site
(D). Able to replicate autonomously
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (C) and (D) only.
• D. (B), (C) and (D) only.

Hint:

When evaluating properties of a biological tool like a vector, distinguish between fundamental requirements (like replication and insertion sites) and desirable features for convenience (like small size or high copy number). The fundamental requirements are always the most important.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A cloning vector is a small piece of DNA that can be stably maintained in an organism, and into which a foreign DNA fragment can be inserted for cloning purposes. A good cloning vector must possess several key features to be useful in molecular biology.
Step 2: Detailed Explanation:
Let's evaluate each listed property:
(A) Ideally should be less than 10 kb: This is a desirable feature for plasmid vectors because smaller DNA molecules are easier to handle, manipulate, and transform into host cells with higher efficiency. However, this is not a universal property of all vectors. For cloning very large DNA fragments, larger vectors like Bacterial Artificial Chromosomes (BACs, 100-300 kb) or Yeast Artificial Chromosomes (YACs, >300 kb) are used. Thus, this is a useful guideline but not a fundamental requirement for all vectors.
(B) Isolation and purification should be easy: This is a crucial practical requirement. For a vector to be useful, it must be possible to easily separate it from the host cell's chromosomal DNA in high quantity and purity.
(C) Should contain a unique target site: This is essential. A vector must have at least one, and preferably many, unique restriction enzyme recognition sites, typically clustered in a Multiple Cloning Site (MCS). A unique site ensures that the restriction enzyme cuts the vector at only one location, allowing the foreign DNA fragment to be inserted.
(D) Able to replicate autonomously: This is the defining characteristic of a vector. It must contain an origin of replication (ori) that allows it to be replicated by the host cell's machinery, independently of the host chromosome. This ensures that the vector and the inserted DNA are propagated and passed on to daughter cells.
Step 3: Final Answer:
Properties (B), (C), and (D) are fundamental and essential characteristics of virtually all cloning vectors. Property (A) is a desirable feature for efficiency and convenience, particularly for plasmids, but is not a defining or universal property for all types of vectors. Therefore, the most accurate combination of essential properties is (B), (C), and (D).