Mutation and Selection
One-Sentence Definition
Mutation generates heritable genetic variation; selection (e.g., antibiotics, immunity, environment) changes which variants dominate a population.
Simple Explanation
Random DNA spelling changes happen; whatever survives best under pressure becomes common.
Detailed Scientific Explanation
- Spontaneous mutations: substitutions, indels, frameshifts; also phase variation / hypermutators (mismatch repair defects).
- Antibiotics do not cause specific resistance mutations on purpose — they select pre-existing or arising resistant cells.
- Vertical evolution complements Horizontal Gene Transfer.
- Fitness trade-offs: resistance alleles may slow growth (Bacterial Growth Curve) unless compensated.
Mechanism
DNA replication errors / damage → mutant subpopulation → differential survival under selective agent → clonal expansion. Population bottlenecks and biofilms shape outcomes.
Clinical Importance
- On-therapy resistance (e.g., fluoroquinolones, rifampin monotherapy in TB risk context).
- Combination therapy and adequate dosing reduce selective escape.
Research Importance
- Experimental evolution, Luria–Delbrück logic, MIC creep studies.
Diagnostic Relevance
- AST detects selected phenotypes; WGS finds resistance-associated mutations (e.g., gyrA, rpoB).
AMR Relevance
- Chromosomal resistance (target modification, regulatory mutations for efflux) plus HGT of resistance genes = full AMR picture.
Related Methods
Related MOCs
Active Recall Questions
- Do antibiotics create resistance mutations, or select them?
- Give an example of target-site mutation resistance.
- How can hypermutators accelerate AMR evolution?
Connections
- With mobile DNA: Horizontal Gene Transfer · Plasmid