A population of moths lives in a woodland area. Some moths have a pale wing colour and some have a dark wing colour. Over several generations, the proportion of dark-winged moths in the population increases. Explain how natural selection could account for this change in the population of moths.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
There is variation in wing colour within the moth population – some moths are pale and others are dark.
Dark wing colour is an advantageous phenotype because it provides better camouflage from predators in the woodland.
As a result, dark‑winged moths are more likely to survive and reproduce, passing the advantageous allele to their offspring.
Over many generations the frequency of the allele for dark wing colour increases in the population.
Dark wing colour is an advantageous phenotype because it provides better camouflage from predators in the woodland.
As a result, dark‑winged moths are more likely to survive and reproduce, passing the advantageous allele to their offspring.
Over many generations the frequency of the allele for dark wing colour increases in the population.
Examiner tips
- Use the word ‘variation’ to show the first point. Explain why dark colour is advantageous (camouflage).
- Show the link between survival, reproduction and allele transmission. Mention that the change occurs over many generations.
Common mistakes
- Failing to state that variation exists. Not linking camouflage to survival. Using vague terms like ‘better suited’ without explanation.
Mark scheme (4 marks)
- There is variation in wing colour within the moth population (pale and dark)
- Dark wing colour is an advantageous phenotype / dark-winged moths are better suited to the environment (e.g. better camouflaged from predators)
- Dark-winged moths are more likely to survive and reproduce, passing the advantageous allele on to offspring
- Over many generations, the frequency of the advantageous allele (dark wing colour) increases in the population
Key terms in this question
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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