Which statement best describes a plasmid backbone and factors influencing its stability in bacterial expression systems?

Which statement best describes a plasmid backbone and factors influencing its stability in bacterial expression systems?

• A. A plasmid backbone is simply a random DNA fragment with no role in replication or selection.
• B. The plasmid backbone may carry a selection marker, but replication origin is optional.
• C. Copy number has no influence on stability or yield.
• D. A plasmid backbone provides replication origin and selection markers; copy number influences yield and metabolic burden; stability depends on origin, selective pressure, and host.

Answer: (D)