Explain why individuals with greater reproductive success are more likely to pass on their alleles to future generations, and how this leads to a change in allele frequency in a population over time.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Individuals with favourable traits survive longer or reproduce more successfully, producing more offspring.
Offspring inherit alleles from parents, so favourable alleles are transmitted to the next generation at a higher rate than unfavourable alleles.
Over successive generations the frequency of favourable alleles rises in the population while unfavourable alleles fall.
This cumulative change in allele frequency across generations is the mechanism of natural selection, driving adaptation.
Offspring inherit alleles from parents, so favourable alleles are transmitted to the next generation at a higher rate than unfavourable alleles.
Over successive generations the frequency of favourable alleles rises in the population while unfavourable alleles fall.
This cumulative change in allele frequency across generations is the mechanism of natural selection, driving adaptation.
Examiner tips
- Use the word "favourable" or "advantageous" to show understanding of selection pressure.
- Show the link between survival/reproduction and allele transmission.
- Mention that the change is cumulative over generations.
- Keep the answer concise – 4 short sentences are enough for full marks.
Common mistakes
- Confusing survival with reproduction – both contribute to reproductive success.
- Using vague terms like "better" without specifying "favourable" or “advantageous”.
- Failing to mention that the change is cumulative over generations.
Mark scheme (4 marks)
- Individuals with favourable traits/alleles survive longer or reproduce more successfully, leaving more offspring.
- Offspring inherit alleles from parents, so favourable alleles are transmitted to the next generation at a higher rate than unfavourable alleles.
- Over successive generations, the frequency of favourable alleles increases in the population (and unfavourable alleles decrease).
- This cumulative change in allele frequency across generations is the mechanism of natural selection, potentially leading to adaptation of the population.
Key terms in this question
reproductive success · allele frequency
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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