Explain why sexual reproduction in animals produces offspring that are not genetically identical to either parent.

Pearson Edexcel A-Level Biology A (9BI0) — 2.3 Sexual reproduction in animals and plants · Explain · 5 marks · View as Markdown

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

Sexual reproduction involves the fusion of two gametes to form a zygote. Gametes are produced by a process that results in haploid cells.

Model answer (5 marks)

Gametes are haploid, each containing a single copy of every chromosome.
Gametes are produced by two different parents, so one gamete comes from each.
Fertilisation fuses the two gametes to form a diploid zygote.
The zygote therefore contains a combination of chromosomes from both parents.
Because the combination of genetic material varies with each fertilisation, the offspring are not genetically identical to either parent.

Examiner tips

  • Use the exact terms ‘haploid’, ‘diploid’, ‘gamete’, ‘zygote’.
  • Show the flow: haploid gametes → fertilisation → diploid zygote with mixed DNA.
  • Explain that variation comes from the random pairing of parental chromosomes.

Common mistakes

  • Confusing ‘haploid’ with ‘diploid’ for gametes.
  • Saying offspring are identical to one parent instead of explaining mixing.
  • Omitting the step that fertilisation creates a diploid zygote.

Mark scheme (5 marks)

  1. Gametes are haploid / contain a single copy of each chromosome
  2. Gametes are produced from two different parents / one gamete from each parent
  3. Fertilisation / fusion of gametes produces a diploid zygote
  4. The zygote contains a combination of genetic material / chromosomes from both parents
  5. This mixing of genetic material / variation in which gametes fuse means offspring are not genetically identical to either parent

Related

More Sexual reproduction in animals and plants questions

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