# Explain how the construction of a cladogram uses shared derived characters (synapomorphies) to determine evolutionary relationships between organisms.

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

> Cladistics is a method of biological classification that groups organisms based on common ancestry, using observable characteristics to infer phylogenetic relationships.

## Mark scheme (4 marks)

1. Synapomorphies are shared derived characters that are inherited from a common ancestor and are used to group organisms into clades.
2. Organisms that share more synapomorphies are considered more closely related and are placed closer together / in the same clade on the cladogram.
3. Each branching point (node) on a cladogram represents a hypothetical common ancestor at which a new derived character first appeared.
4. Cladograms are constructed using the principle of parsimony, selecting the tree that requires the fewest evolutionary changes to explain the distribution of characters observed.

## Key terms

- [cladogram](https://www.gradenine.co.uk/glossary/cladogram)
- [shared derived character](https://www.gradenine.co.uk/glossary/shared-derived-character)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-construction-of-a-2c1d8e51) · Published by Druglandscape Ltd.