# Explain the concept of a synapomorphy and outline how shared derived characters are used to group organisms into clades.

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

## Mark scheme (4 marks)

1. A synapomorphy is a shared derived character (trait) that is inherited from a common ancestor and is present in all members of a clade but not in organisms outside that clade.
2. Shared derived characters are distinguished from ancestral (plesiomorphic) characters, which are inherited from a more distant ancestor and shared more broadly — only derived characters support grouping into a clade.
3. Organisms that share one or more synapomorphies are grouped together into a clade because the shared derived character is evidence of descent from a common ancestor in which the character first evolved.
4. Multiple synapomorphies can be used to define nested clades, so that smaller clades (sharing more recent derived characters) are contained within larger clades (sharing older derived characters), reflecting evolutionary history.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-the-concept-of-a-synapomorphy-4b0d13ce) · Published by Druglandscape Ltd.