Which class of mutations arises in the absence of deliberate exposure to external mutagenic agents, originating instead from normal cellular processes such as replication errors or spontaneous base alterations?

Introduction / Context:
Mutations can originate without any intentional treatment. Cells constantly face endogenous sources of DNA change, including replication slippage, tautomeric shifts, oxidative damage, and depurination. Distinguishing spontaneous from induced mutations is a basic classification in genetics and microbial mutagenesis.

Given Data / Assumptions:

• No external physical or chemical mutagens are applied.
• Endogenous processes are capable of altering DNA.
• Terminology follows standard genetics usage.

Concept / Approach:
Spontaneous mutations arise naturally during the life of a cell. DNA polymerases have finite fidelity and, despite proofreading and mismatch repair, occasional errors persist. Hydrolytic reactions such as deamination of cytosine to uracil or depurination create abasic sites; reactive oxygen species can oxidize bases like guanine to 8 oxoguanine, leading to mispairing. These events occur without external triggers.

Step-by-Step Solution:
Identify that no external agent is present. List endogenous mechanisms that can cause base changes or insertions and deletions. Map the definition to the correct term: spontaneous mutations. Exclude induced mutations which require a mutagen.

Verification / Alternative check:
Fluctuation tests show mutation occurrence before selection pressure, consistent with spontaneous origin rather than induced change during selection.

Why Other Options Are Wrong:

• Analogous mutations: not a recognized category in this context.
• Induced mutations: require exposure to mutagens like UV or alkylating agents.
• None of these: incorrect because a standard term exists.

Common Pitfalls:
Assuming all mutations are environmentally driven; baseline mutation rates persist due to intrinsic biochemical processes.

Final Answer:
Spontaneous mutations