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A-Level Biology May/June 2025 Q3(b): Suggest and explain why variegate porphyria is more common among people of Dutch descen…
A-Level Biology · Paper 9700/41 · May/June 2025 · Question 3(b) · [3 marks]
Suggest and explain why variegate porphyria is more common among people of Dutch descent in South Africa than among people in Europe.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
- accepted ✓
This is an example of the founder effect. [1]
A small population of Dutch settlers migrated to South Africa. By chance, this founding population included individuals who carried the allele for variegate porphyria. [2]
As a result, the frequency of this allele in the small founding gene pool was significantly higher than in the original, larger Dutch population in Europe. [3] The population remained relatively isolated for many generations, meaning the high frequency of the allele was maintained, leading to a greater prevalence of the disorder compared to people in Europe.
How the marks are awarded
- M1 — Correctly identifying the phenomenon as the 'founder effect'.
- M1 — Stating that the allele for variegate porphyria was present in the original small group of Dutch settlers/migrants.
- M1 — Explaining that the allele frequency was higher in the founding population than in the original European population.
Common mistakes
- Simply stating 'genetic drift' without specifying the founder effect, which is the more precise answer for this scenario.
- Incorrectly suggesting that the allele conferred a selective advantage, which would be natural selection, not a chance event like the founder effect.
- Failing to mention that the founding population was small and/or reproductively isolated, which are key conditions for the founder effect to have a significant impact.
- Describing the events but failing to use the key term 'founder effect' and thus missing a straightforward mark.
Examiner tip: When a question describes a new population being established by a small number of individuals from a larger parent population, always consider the founder effect as the primary explanation for any unusual allele frequencies.
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