Describe the differences between continuous variation and discontinuous variation, giving one example of each type.

Cambridge International IGCSE Biology (0610) — 18.1 Variation · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Continuous variation shows a range of phenotypes between two extremes and cannot be placed into distinct categories. Discontinuous variation shows distinct categories or a limited number of discrete groups. Continuous variation is influenced by both genes and environmental factors, whereas discontinuous variation is generally influenced by genes alone. An example of continuous variation is human height. An example of discontinuous variation is the colour of pea flower petals (e.g. red or white).

Examiner tips

  • Use the exact terms ‘continuous’ and ‘discontinuous’ variation. Mention the key differences: range vs distinct groups, gene + environment vs gene alone. Give one clear example for each type. Keep the answer concise to fit the 4‑mark limit.

Common mistakes

  • Confusing the definition of continuous with that of discontinuous. Giving an example that is not clearly continuous or discontinuous (e.g. colour of human eyes). Omitting the environmental factor for continuous variation or the gene‑only point for discontinuous variation.

Mark scheme (4 marks)

  1. Continuous variation produces a range of phenotypes between two extremes / cannot be placed into distinct categories
  2. Discontinuous variation produces distinct categories / a limited number of discrete groups
  3. Continuous variation is influenced by both genes and environmental factors; discontinuous variation is generally influenced by genes alone
  4. A correct example of continuous variation AND a correct example of discontinuous variation

Key terms in this question

continuous variation · discontinuous variation

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