# Explain how the construction of a cladogram differs from classical Linnaean classification in the way that shared characteristics are used to group organisms.

> IB DP Biology Higher Level (2023 syllabus) — A3.2 Classification and cladistics · Explain · 4 marks

## Mark scheme (4 marks)

1. Cladistics groups organisms based on shared derived characteristics (synapomorphies), whereas Linnaean classification may use overall similarity / shared ancestral characteristics (symplesiomorphies).
2. In cladistics, only characteristics that arose in a common ancestor and are shared exclusively by its descendants (defining a clade) are used to determine branching points / nodes.
3. Linnaean classification assigns organisms to hierarchical ranked taxa (kingdom, phylum, class, order, family, genus, species) based on morphological / physiological criteria that may not reflect evolutionary relationships, whereas cladograms represent evolutionary / phylogenetic relationships without requiring fixed ranks.
4. Convergent / analogous characteristics can lead to incorrect groupings in classical classification, whereas cladistics avoids this by distinguishing homologous derived characters from analogous ones, making groups more reflective of true common ancestry.

## Key terms

- [cladogram](https://www.gradenine.co.uk/glossary/cladogram)
- [Linnaean classification](https://www.gradenine.co.uk/glossary/linnaean-classification)

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