Explain why two geographically isolated populations of the same species may, over many generations, develop different adaptations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A species of small mammal originally lived across a large continent. A mountain range formed over thousands of years, splitting the population into two groups that could no longer interbreed. Scientists observed that the two groups gradually developed different physical characteristics.
Model answer (5 marks)
1. The two populations live in different environments, so they face different selection pressures.
2. Random mutations generate new alleles, creating genetic variation within each group.
3. Individuals carrying alleles that give an advantage in their local environment are more likely to survive and reproduce.
4. Those advantageous alleles are passed on to offspring, so their frequency rises in that population.
5. Because the populations are geographically isolated and cannot interbreed, the advantageous alleles accumulate separately, leading to different adaptations.
2. Random mutations generate new alleles, creating genetic variation within each group.
3. Individuals carrying alleles that give an advantage in their local environment are more likely to survive and reproduce.
4. Those advantageous alleles are passed on to offspring, so their frequency rises in that population.
5. Because the populations are geographically isolated and cannot interbreed, the advantageous alleles accumulate separately, leading to different adaptations.
Examiner tips
- Use the word ‘selection pressure’ and ‘advantageous allele’ – these are key terms. Show the causal chain: environment → mutation → selection → allele frequency change → isolation. Keep each point short and to the point, matching the 5 marks.
- common_mistakes
- :
- Mixing up ‘mutation’ with ‘selection’ or not recognising that isolation prevents gene flow. Using vague phrases like ‘different traits’ without linking them to selection and allele frequency changes.
Mark scheme (5 marks)
- Each population experiences different environmental conditions / selection pressures
- Random mutations produce new alleles / genetic variation within each population
- Individuals with alleles that are advantageous in their local environment are more likely to survive and reproduce
- Advantageous alleles are passed on to offspring, increasing in frequency in that population
- Because the two populations are isolated they cannot interbreed, so different alleles / adaptations accumulate separately in each population
Key terms in this question
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →