Explain how analogous structures and homologous structures differ in their usefulness for constructing cladograms.

IB DP Biology Standard Level (2023 syllabus) — A3.2 Classification and cladistics · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Homologous structures are derived from a common ancestor and therefore indicate shared evolutionary history. They can be used as synapomorphies to construct accurate cladograms. Analogous structures perform the same function but evolved independently in different lineages through convergent evolution; they do not reflect shared ancestry and would mislead cladogram construction.

Examiner tips

Use the terms ‘homologous’ and ‘analogous’ explicitly. State that homologous traits are synapomorphies. Explain that analogous traits arise by convergent evolution and are misleading. Keep the answer concise to fit the 4‑mark limit.

Common mistakes

Confusing homology with analogy. Failing to mention convergent evolution for analogous traits. Using vague language like ‘similar’ without specifying evolutionary origin.

Mark scheme (4 marks)

Homologous structures are derived from a common ancestor / shared evolutionary origin
Homologous structures reflect true evolutionary relationships and are therefore useful for constructing cladograms / as synapomorphies
Analogous structures perform the same function but evolved independently in different lineages / are the result of convergent evolution
Analogous structures do not reflect shared ancestry and so would lead to incorrect groupings / are not useful / can be misleading in cladogram construction

Key terms in this question

homologous structures · analogous structures · cladogram