Explain why sexual reproduction generates greater genetic variation in offspring than asexual reproduction.

IB DP Biology Standard Level (2023 syllabus) — D3.1 Reproduction · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Sexual reproduction generates greater genetic variation because it involves the fusion of two gametes, so offspring receive DNA from two parents. Meiosis creates genetically unique gametes through independent assortment of homologous chromosomes, and crossing‑over during meiosis I produces recombinant chromosomes, giving new allele combinations. In contrast, asexual reproduction relies only on mitosis, producing offspring that are clones of the parent with no new genetic combinations.

Examiner tips

  • Mention fertilisation and two parents first
  • Explain independent assortment and crossing‑over
  • Contrast with mitosis and cloning
  • Use exact terms: gametes, meiosis, independent assortment, crossing‑over

Common mistakes

  • Confusing mitosis with meiosis as the source of variation
  • Failing to mention fertilisation or the role of two parents
  • Using vague terms like ‘mixing’ instead of ‘crossing‑over’

Mark scheme (4 marks)

  1. Sexual reproduction involves the fusion of two gametes (fertilisation), combining genetic material from two parents
  2. Meiosis produces genetically unique gametes through independent assortment of homologous chromosomes
  3. Crossing over during meiosis I produces recombinant chromosomes, generating new allele combinations
  4. Asexual reproduction produces offspring that are genetically identical to the parent (clones), as only mitosis is involved and there is no fusion of gametes

Key terms in this question

sexual reproduction · asexual reproduction · genetic variation

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