# Explain how molecular sequence data can be used to determine whether two species belong to the same clade.

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

## Mark scheme (4 marks)

1. DNA (or amino acid / protein) sequences are compared between the two species and an outgroup
2. Shared derived characters (synapomorphies) / shared sequence similarities that are not present in the outgroup indicate common ancestry
3. The greater the proportion of shared sequence differences (relative to an outgroup), the more recently the two species diverged / the more closely related they are
4. A cladogram is constructed placing the two species in the same clade if they share a more recent common ancestor with each other than with any other group / the outgroup

## Key terms

- [clade](https://www.gradenine.co.uk/glossary/clade)
- [molecular sequence data](https://www.gradenine.co.uk/glossary/molecular-sequence-data)

## 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-how-molecular-sequence-data-can-92e19f16) · Published by Druglandscape Ltd.