Regulatory genetics: a phosphate-deregulated mutant (Pho– derepressed) is best described as being:

Introduction / Context:
Phosphate regulation systems (e.g., Pho regulon in bacteria) control expression of genes in response to phosphate availability. Mutations can alter the sensitivity of this control, affecting metabolite uptake and enzyme production.

Given Data / Assumptions:

• A deregulated mutant exhibits constitutive or reduced-control expression.
• Environmental phosphate usually represses certain genes; scarcity derepresses them.
• Terminology: deregulated/derepressed implies diminished responsiveness.

Concept / Approach:
In deregulated (derepressed) mutants, the normal repression by phosphate is weakened or lost, so target genes are expressed even when phosphate would ordinarily repress them. This corresponds to being less sensitive to phosphate-mediated regulation.

Step-by-Step Solution:

Verification / Alternative check:
Phenotypes such as constitutive alkaline phosphatase activity in the presence of phosphate exemplify deregulation.

Why Other Options Are Wrong:
Moderately or highly sensitive: Opposite of deregulated behavior. None of these: Incorrect because a precise description exists.

Common Pitfalls:
Confusing derepression (reduced control) with hypersensitivity (increased control).

Final Answer:
less sensitive to phosphate regulation