KHAEMENES ACADEMY · BIOLOGY 10 · WEEK 28 · DAY 04

Gene Flow, Mutation & Selection as Distinct Mechanisms

Compare mechanisms by the kind of change they introduce rather than labeling all frequency change “natural selection.”

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

Gene flow moves alleles among populations through migration and reproduction. Mutation creates new sequence variants. Selection changes frequencies when heritable variants differ in reproductive contribution. Drift changes frequencies stochastically.

Several mechanisms can act simultaneously, and the same observed frequency change can have multiple plausible causes.

Worked example with reasoning

Population A has allele X=.2 and B has X=.8. Migration from B into A raises X in A before any fitness difference is measured: gene flow is sufficient to explain the immediate change. If X carriers later leave more offspring, selection may also contribute.

Guided question

What evidence would help distinguish gene flow from selection?

Independent work

  1. Match four datasets to mechanisms.
  2. For one dataset, propose two alternative mechanisms.
  3. Identify evidence needed to distinguish them.
  4. Explain mutation's special role in creating new alleles.

Investigation / Data Lab

Allele-frequency simulation

Question: How do drift, migration, or selection change allele frequency trajectories under different model rules?

  1. Begin at p(A)=0.50 with a defined population size using cards, coins, or a spreadsheet.
  2. Run a control with random sampling only, then a treatment changing exactly one mechanism.
  3. Record p(A) for at least ten generations and repeat each condition several times.
  4. Graph all trajectories rather than only the most dramatic run.
  5. Compare mean direction and run-to-run variability, then state which mechanism claim is supported by the model.

Evidence standard: preserve rules, population size, raw trajectories, graph, and stochastic-variation statement.

Misconception check

Natural selection is not the only evolutionary mechanism, and not every allele-frequency increase is adaptation.

Formative understanding check

Which mechanism directly introduces a new allele sequence?

Worked response

Mutation.

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 Archaemenes

Teacher guidance

Foundation: use mechanism cards. Core: justify mechanism from evidence. Extended: model simultaneous drift, flow and selection conceptually.

Preserve learning evidence

Keep calculations, graphs, models, corrections and limitations in the matching Week 28 evidence field.