Describe how meiosis and fertilisation together ensure that offspring produced by sexual reproduction are genetically different from their parents.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Meiosis produces haploid gametes, each containing half the chromosome number of the parent.
During meiosis, homologous chromosomes exchange genetic material (cross‑over) and the two daughter cells receive different combinations of alleles, so the gametes are genetically distinct.
Fertilisation is the fusion of a male and a female gamete; the nuclei combine to form a diploid zygote.
Because the gametes are random combinations of alleles from two parents, fertilisation creates a unique genetic mix, giving offspring a different genotype to either parent.
During meiosis, homologous chromosomes exchange genetic material (cross‑over) and the two daughter cells receive different combinations of alleles, so the gametes are genetically distinct.
Fertilisation is the fusion of a male and a female gamete; the nuclei combine to form a diploid zygote.
Because the gametes are random combinations of alleles from two parents, fertilisation creates a unique genetic mix, giving offspring a different genotype to either parent.
Examiner tips
- Use the words ‘haploid’ and ‘diploid’ to show understanding of chromosome numbers.
- Mention cross‑over as a source of variation.
- Explain that fertilisation restores the diploid number and combines two different gametes.
- Keep the answer concise – 4 points can be covered in 4 short sentences.
Common mistakes
- Failing to state that meiosis produces haploid cells.
- Not mentioning cross‑over or random assortment as sources of variation.
- Confusing fertilisation with meiosis or omitting that it restores the diploid number.
Mark scheme (4 marks)
- Meiosis produces gametes / sex cells that are haploid (contain half the chromosome number)
- Meiosis produces gametes that are genetically different from one another / genetic variation is introduced during meiosis
- Fertilisation is the fusion of a male and female gamete / their nuclei fuse
- Fertilisation randomly combines alleles from two different parents, producing a new genetic combination / restores the diploid number with a unique mix of alleles
Key terms in this question
Related
- All Edexcel GCSE Biology (1BI0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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