Genetics and mutations — When a mutation disrupts vital cellular functions such that the mutated organisms cannot survive or reproduce, this type of mutation is called:

Introduction / Context:
Mutations can range from silent changes to alterations that fundamentally impair life processes. In genetics and microbiology, it is essential to distinguish between different mutation classes, because each has different biological consequences and implications for viability, inheritance, and disease.

Given Data / Assumptions:

• The question asks about mutations that affect vital functions to the extent that mutants cannot live (nonviable).
• We compare this definition with other common mutation terms such as nonsense mutation and transversion.
• We assume standard genetics terminology used in microbiology and molecular biology.

Concept / Approach:
Mutations are categorized by molecular change (e.g., base substitution, insertion, deletion) or by effect (e.g., silent, missense, nonsense, lethal). A lethal mutation is defined by its phenotypic outcome: it prevents survival or reproduction because an essential gene, pathway, or structural element is compromised. By contrast, a nonsense mutation introduces a stop codon prematurely; it may or may not be lethal depending on the gene. A transversion is a type of base substitution (purine ↔ pyrimidine) and has no inherent lethality without context.

Step-by-Step Solution:

Verification / Alternative check:
Classic examples include null mutations in genes encoding essential DNA replication proteins or ribosomal components; such mutants cannot form colonies, confirming lethality.

Why Other Options Are Wrong:

• Nonsense mutation: introduces a stop codon; sometimes lethal, sometimes not.
• Transversion: describes a substitution type, not the viability outcome.
• None of these: incorrect because “lethal mutation” is the standard term.

Common Pitfalls:
Equating a specific molecular change (e.g., nonsense) with an outcome (lethality). The same molecular change can be benign or lethal depending on the affected gene.

Final Answer:
lethal mutation