Explain how the reclassification of organisms using molecular evidence has changed our understanding of evolutionary relationships, using one named example.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Traditional classification relied on morphology, which could group unrelated species together.
Molecular data (DNA, gene, amino‑acid sequences) reveal true evolutionary relationships.
This evidence has caused reclassification, moving species between taxa and uniting previously separate groups.
Example: whales were reclassified as artiodactyls, most closely related to hippos, based on DNA analysis.
Molecular data (DNA, gene, amino‑acid sequences) reveal true evolutionary relationships.
This evidence has caused reclassification, moving species between taxa and uniting previously separate groups.
Example: whales were reclassified as artiodactyls, most closely related to hippos, based on DNA analysis.
Examiner tips
- Use the word "molecular" and give a specific example; link the example to the reclassification point; keep answer concise to fit 4 marks.
- Mention both the old and new classification to show understanding of change.
Common mistakes
- Confusing morphology with molecular evidence; not naming a specific example; giving an example that is not from the IB syllabus.
Mark scheme (4 marks)
- Traditional classification was based on morphology / observable physical characteristics, which could lead to grouping organisms that appear similar but are not closely related
- Molecular evidence such as DNA base sequences / gene sequences / amino acid sequences can reveal true evolutionary relationships / degree of common ancestry
- Molecular evidence has led to reclassification, with some organisms moved to different taxa / groups previously thought to be related separated / groups previously thought to be unrelated united
- Named example correctly used — e.g. giant pandas reclassified from Procyonidae (raccoon family) to Ursidae (bear family) based on molecular data; OR fungi reclassified from Plantae to their own kingdom Fungi based on molecular/biochemical evidence; OR whales shown by molecular evidence to be most closely related to hippos / artiodactyls; OR birds reclassified as a clade within reptiles (Reptilia) based on molecular and phylogenetic evidence
Key terms in this question
reclassification · molecular evidence · evolutionary relationships
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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