Change across generations.

Mutation and recombination produce heritable variation. If a variant affects survival or reproduction in a particular environment, its frequency may change across generations. Natural selection acts on phenotypes, while evolution is measured as a change in population allele frequencies.

Selection is not the only process: genetic drift, migration and mutation also shift allele frequencies. A trait advantageous in one environment may be disadvantageous in another. Individuals do not genetically evolve during their own lifetime.

INTERACTIVE MODEL

Allele frequency

Allele A: 25% → 42.3% after 10 model generationsRelative advantage of A8−20%+20%

Explore: Change the advantage of one phenotype and follow allele frequency over generations.

p+q=1\qquad\Delta p=p_{t+1}-p_t

WORKED EXAMPLE

An allele rises from frequency 0.20 to 0.35.

Subtract 0.20 from 0.35.
Its frequency changed by +0.15 across the measured interval.

Assumed knowledge

Proportions and inheritance.

Learning checkpoints & source

YOUR LEARNING CHECKPOINT

Connect variation, selection and allele frequencies.
Distinguish individual adaptation from evolution.

QCAA Biology · Unit 4 · Continuity of life on Earth ↗

READY TO TRY IT?

Change across generations.

Allele frequency

An allele rises from frequency 0.20 to 0.35.

Put the idea to work.