Plasmid copy number terminology Plasmids maintained at multiple copies per cell are commonly referred to as which class?

Introduction / Context:
Plasmids differ in copy number control. This feature influences gene expression level, plasmid stability, and the yield of recombinant products in biotechnology. Correct terminology helps interpret cloning manuals and research papers.

Given Data / Assumptions:

• Some plasmids replicate to many copies (high copy number), others to few (low copy number).
• Copy number is governed by the plasmid origin and its regulatory circuitry.
• Terms “stringent” and “relaxed” are historically used to describe this behavior.

Concept / Approach:
“Relaxed” control permits many replication initiations, leading to high copy numbers (often tens to hundreds per cell). “Stringent” control ties replication more tightly to the cell cycle, yielding low copy numbers (often 1–2 per chromosome equivalent). “Cryptic” refers to plasmids lacking obvious selectable phenotypes, not copy number per se.

Step-by-Step Solution:

Verification / Alternative check:
Classic examples include pUC (relaxed, high copy) versus F-type plasmids (stringent, low copy). Vendor datasheets confirm this terminology.

Why Other Options Are Wrong:

• Stringent plasmids are typically low copy.
• Cryptic plasmids lack obvious traits; copy number may vary.
• Other labels (conditional, mini-F) do not define high copy status.

Common Pitfalls:
Assuming high copy always yields higher protein; expression can be limited by toxicity or translation resources.

Final Answer:
Relaxed plasmids