Explain how the discovery of DNA helped scientists to understand evolution and classification. Include how this changed the way organisms were grouped.

AQA GCSE Biology (8461) — 4.6.3 The development of understanding of genetics and evolution · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

DNA carries the genetic information that can be compared between organisms.

Similarities in DNA sequences show common ancestry and help map evolutionary relationships.

DNA evidence led to the three‑domain system (Archaea, Bacteria, Eukaryota) proposed by Carl Woese.

Thus classification shifted from grouping by physical traits to grouping by molecular (DNA) similarity.

Examiner tips

  • Use the word ‘DNA’ and ‘genetic information’ early. Show the link between DNA similarity and common ancestry. Mention the three‑domain system. Explain the shift from morphology to molecular classification.

Common mistakes

  • Confusing DNA with RNA or proteins. Failing to mention the three‑domain system. Stating that DNA proved evolution without linking to classification changes.

Mark scheme (4 marks)

  1. DNA carries genetic information / genetic code that can be compared between organisms
  2. Similarities in DNA sequences between organisms indicate common ancestry / evolutionary relationships
  3. DNA evidence led to the development of the three-domain system (by Carl Woese) / organisms reclassified into Archaea, Bacteria and Eukaryota
  4. This changed classification because organisms previously grouped by physical appearance / observable characteristics alone were reclassified using molecular / DNA evidence

Key terms in this question

DNA · evolution · classification

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