conditionally lethal mutant

con·di·tion·al·ly le·thal mu·tant

a viral mutant that can replicate under some (permissive) conditions but not under other (restrictive or nonpermissive) conditions, the parent (wild-type) strain being able to replicate under both conditions. See: suppressor-sensitive mutant, temperature-sensitive mutant. Synonym(s): conditional-lethal mutant