Which statement best describes constitutive gene expression?

• A. Turned on only under stress
• B. Always on
• C. Requires inducer to activate
• D. Always off

Answer: (B)

Constitutive gene expression means genes are transcribed continuously, providing essential cellular functions and not needing specific signals to be turned on. They run at a relatively constant level to keep basic processes like metabolism and maintenance going. That’s why describing them as always on best captures the idea: their expression doesn’t depend on environmental cues or inducers.

The other scenarios describe regulated expression. Genes that turn on only under stress respond to signals indicating stress (inducible). Requiring an inducer to activate is a hallmark of inducible regulation. Always off would mean no expression at all, which contradicts constitutive activity.