# Explain why scientists compare the base sequences of DNA from different species when classifying organisms, and describe what a high percentage of shared base sequences suggests about two species.

> AQA A-Level Biology (7402) — 3.4.7 Investigating Diversity · Explain · 5 marks

> Scientists can now analyse the base sequences of DNA from different organisms. This information is used alongside physical and behavioural characteristics when classifying species and investigating biodiversity.

## Mark scheme (5 marks)

1. DNA base sequences (or the order of bases) carry genetic information / determine characteristics
2. Closely related species share more similar / more base sequences in common
3. DNA evidence is more reliable / objective than using physical characteristics alone (because physical features can be misleading / convergent evolution can make unrelated species look similar)
4. A high percentage of shared base sequences suggests the two species share a recent common ancestor
5. Over time, mutations cause base sequences to change / diverge, so species that separated longer ago have fewer shared sequences

## Key terms

- [base sequence](https://www.gradenine.co.uk/glossary/base-sequence)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-scientists-compare-the-base-a513fc7c) · Published by Druglandscape Ltd.