What is the role of the origin of replication in a plasmid?

• A. Provides antibiotic resistance
• B. Allows plasmid replication in host cells
• C. Serves as promoter for gene
• D. Codes for a fluorescent protein

Answer: (B)

The main idea is that the origin of replication is the site where plasmid DNA replication begins in the host cell. This sequence is recognized by the host’s replication machinery, allowing the plasmid to duplicate and be passed on to daughter cells during cell division. It also influences how many copies of the plasmid are made (copy number) and whether the plasmid can replicate in a given host species (host range). Because enabling replication is the essential role of this region, it is the correct answer.

The other features listed—antibiotic resistance genes, promoters, and fluorescent protein genes—do not drive replication initiation. They provide survival in selective conditions or drive gene expression or reporting, but they don’t initiate the plasmid’s replication.