AP Syllabus focus:
‘Mutations arise randomly and are not directed by specific environmental pressures or needs.’
Mutations create new genetic variation, but the environment does not “cause” helpful mutations to appear on demand. Instead, environmental conditions change which existing variants leave more offspring, shifting allele frequencies over generations.
Core idea: randomness vs selection
Random origin of mutations
Mutations are changes in DNA sequence that occur due to errors and chance events, not because an organism “needs” a trait. They can occur in any environment and in any direction relative to an organism’s current challenges.
Mutation: A heritable change in the nucleotide sequence of DNA.
Practice Questions
FAQ
Yes. Stress responses can alter DNA repair or replication fidelity, raising mutation rate broadly.
The resulting mutations are still random with respect to what would be beneficial.
Random mutations differ between populations.
Selection can favour different alleles or pathways that produce similar resistant phenotypes.
No. Mutation rates vary with DNA sequence context, replication timing, and repair efficiency.
“Random” means not directed towards usefulness, not uniform across sites.
A mutation is a DNA change in an individual.
An adaptation is a heritable trait that becomes common because it increases fitness under certain conditions.
Yes; fitness depends on context.
If conditions change, selection may favour different alleles, including those previously neutral or disadvantageous.
