Safety and evidence boundary
Use fictional populations, cards, spreadsheets, or published aggregate data. Do not use population-genetic concepts to rank human groups or infer personal ancestry, intelligence, worth, or disease. Evolutionary mechanisms are population-level processes.
Explicit science instruction
Genetic drift is random change in allele frequencies due to finite sampling of individuals and gametes. It is strongest in small populations. A bottleneck sharply reduces population size; a founder effect occurs when a new population begins from a small subset.
Drift can increase or decrease an allele regardless of whether it improves fitness.
Worked example with reasoning
A population has A frequency .5. Ten individuals found an island population and, by chance, carry A at .8. The founder population begins different without selection. Later random sampling can push frequency further.
Guided question
How can an allele become common without being advantageous?
Independent work
- Run a coin/card drift simulation for N=10 and N=100.
- Compare frequency variability.
- Model a bottleneck.
- Explain why lost alleles may not return without mutation or gene flow.
Misconception check
Drift is not the same as migration; “genetic drift” does not mean organisms drift geographically.
Formative understanding check
In which population is drift generally stronger: N=20 or N=20,000?
Worked response
N=20.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to challenge whether your population-level claim follows from the data and whether alternative evolutionary mechanisms remain possible.
Open ArchaemenesTeacher guidance
Foundation: use two population-size simulations. Core: compare stochastic outcomes. Extended: analyze effective population size and fixation probability conceptually.
Preserve learning evidence
Keep calculations, graphs, models, corrections and limitations in the matching Week 28 evidence field.