Populations, Selection and Speciation
Allele frequencies, selection pressures, genetic drift, adaptation, reproductive isolation, speciation and evidence for evolutionary change.
How to study A-level Biology
Move between scales deliberately: identify the biological process, trace matter or information, use quantitative evidence, then evaluate the method and conclusion.
Core concepts
Concept 1
Natural selection changes allele frequencies when heritable variation affects survival and reproductive success in a particular environment.
Exam cue: Describe variation first, then selection pressure, differential reproduction, inheritance and frequency change.
Concept 2
Mutation, migration, selection, non-random mating and genetic drift can alter a population's gene pool.
Exam cue: Apply Hardy-Weinberg only when its assumptions are reasonable and define p and q clearly.
Concept 3
Reproductive isolation allows genetic differences to accumulate and may lead to allopatric or sympatric speciation.
Exam cue: Distinguish an organism's acclimatisation from population-level evolution across generations.
Risk pitfalls and guardrails
Saying organisms mutate because they need an adaptation.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Describing evolution as a change within one individual's lifetime.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Treating genetic drift as directional natural selection.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Memory anchors
Natural Selection
Heritable variants with higher reproductive success contribute more alleles to later generations.
Fitness
Evolutionary fitness is reproductive contribution in a particular environment.
Genetic Drift
Genetic drift is random allele-frequency change, strongest in small populations.
Hardy-Weinberg
Under stated assumptions, p + q = 1 and p² + 2pq + q² = 1 for two alleles.
Reproductive Isolation
Barriers to gene flow allow populations to diverge genetically.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
In a beetle population, colour is inherited and dark beetles leave more offspring on soot-darkened bark. Which sequence links this observation to evolutionary change?
What is evolutionary fitness?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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