Explain how molecular sequence data, such as base sequences of DNA or amino acid sequences of proteins, can be used to determine the evolutionary relationships between species.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Species that share a more recent common ancestor will have more similar molecular sequences (DNA or protein). Mutations accumulate over time in molecular sequences at an approximately constant rate, so the number of differences between sequences reflects the time since divergence. Sequence data can be used to construct cladograms / phylogenetic trees that show branching patterns of evolutionary divergence. Molecular data provides an objective, independently verifiable source of evidence that can support or revise classifications based on morphology alone.
Examiner tips
- Use the word ‘explain’ to describe the process, not just state facts.
- Show the link between similarity, mutation rate and time since divergence.
- Mention cladograms/phylogenetic trees as the output of analysis.
- Highlight the objectivity and independent verification of molecular evidence.
Common mistakes
- Confusing similarity with identity; not linking mutation rate to time.
- Failing to mention that molecular data can revise morphology‑based classifications.
- Using vague terms like ‘different’ without explaining how differences indicate divergence.
Mark scheme (4 marks)
- Species that share a more recent common ancestor will have more similar molecular sequences (DNA or protein).
- Mutations accumulate over time in molecular sequences at an approximately constant rate, so the number of differences between sequences reflects the time since divergence.
- Sequence data can be used to construct cladograms / phylogenetic trees that show branching patterns of evolutionary divergence.
- Molecular data provides an objective, independently verifiable source of evidence that can support or revise classifications based on morphology alone.
Key terms in this question
molecular sequence data · amino acid sequence
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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