Explain how a founder effect can influence the genetic diversity and future evolution of a newly established population.

IB DP Biology Higher Level (2023 syllabus) — D4.2 Stability and change · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A founder event occurs when a small number of individuals colonise a new habitat, so the new population contains only a subset of the alleles present in the source population.

Because only a few individuals contribute genes, the new population has reduced genetic diversity and lower allele richness compared with the source.

Allele frequencies in the new population differ from those in the source by chance (sampling error). Some alleles may become unusually common or even lost, while rare alleles may increase in frequency.

The altered allele frequencies and reduced diversity limit the raw material for natural selection, so future evolution may be constrained. This can lead to rapid divergence or speciation, or to an increased prevalence of previously rare recessive conditions in the new population.

Examiner tips

  • Use the word "founder event" first, then explain sampling error and reduced diversity, then link to altered allele frequencies, finally mention evolutionary consequences.
  • Show the logical sequence: colonisation → sampling error → reduced diversity → altered frequencies → evolutionary impact.
  • Include key terms: allele richness, sampling error, random drift, speciation, recessive conditions.

Common mistakes

  • Confusing founder effect with genetic drift in general; not emphasising the initial sampling error.
  • Failing to mention that the new population may have higher frequency of rare alleles or loss of alleles.
  • Using vague terms like "less diversity" without linking to allele richness or frequency changes.

Mark scheme (4 marks)

  1. A founder event occurs when a small number of individuals colonise a new habitat/area, representing only a subset of the original population's alleles.
  2. The new population has reduced genetic diversity / lower allele richness compared to the source population due to this sampling error.
  3. Allele frequencies in the new population differ from the source population by chance / random sampling, so some alleles may be at unexpectedly high or low frequency.
  4. The altered allele frequencies and reduced diversity constrain future evolution, potentially leading to rapid divergence / speciation or increased prevalence of previously rare recessive conditions in the new population.

Key terms in this question

founder effect · genetic diversity

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