Question

Which is true regarding a cosmid vector?

• A. Plaques are not produced
• B. Use lac selection system
• C. Can carry small DNA fragments
• D. Uses lambda origin of replication

Hint:

Cosmids use the lambda origin of replication and can carry large DNA fragments, typically used in genomic libraries.

Answer 1

The Correct Option is D

Step 1: Understanding Cosmid Vectors 
Cosmids are hybrid vectors that combine features of plasmids and phages, allowing for the cloning of large DNA fragments. 
Step 2: Evaluating the Options 
- Plaques are not produced: Incorrect, since cosmid vectors are based on lambda phages, plaques are produced. 
- Use lac selection system: Incorrect, although some vectors use lac operon for selection, this is not a defining feature of cosmids. 
- Can carry small DNA fragments: Incorrect, cosmids are known for carrying larger DNA fragments, up to 40 kb. 
- Uses lambda origin of replication: Correct, cosmids use the lambda origin of replication to replicate in the host cell. 
Step 3: Conclusion 
Cosmids use the lambda origin of replication to ensure they can replicate within bacterial cells.