Explain why scientists now use DNA base sequences, rather than physical characteristics alone, to classify organisms into groups.

Cambridge International IGCSE Biology (0610) — 1.2 Concept and use of a classification system · 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 base sequences give a more accurate measure of evolutionary relatedness because they are inherited directly from common ancestors. The more similar the sequences, the closer the relationship. Organisms in the same habitat can evolve similar morphology by convergent evolution, yet their DNA may be very different. DNA also encodes amino‑acid sequences, so protein structure can corroborate DNA evidence of relatedness.

Examiner tips

Use the exact phrase ‘more accurate measure of evolutionary relationship’
Explain the link between DNA similarity and relatedness
Mention convergent evolution as a limitation of morphology alone
Show that DNA determines protein structure, providing extra evidence

Common mistakes

Confusing DNA similarity with physical similarity; ignoring convergent evolution
Using vague terms like ‘similar’ without linking to evolutionary relatedness
Failing to mention that DNA codes for proteins

Mark scheme (4 marks)

DNA base sequences provide a more accurate measure of evolutionary relationship / relatedness between organisms
The more similar the DNA base sequences, the more closely related the organisms
Different species living in the same habitat may evolve similar physical characteristics / morphology (but not be closely related)
DNA codes for the amino acid sequence in proteins, so protein structure can also be used as evidence of evolutionary relationships

Key terms in this question

DNA base sequence · physical characteristics

More Concept and use of a classification system questions

▶ Try answering this question with AI marking (free) →