AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Students should be able to explain how meiosis halves the number of…
Full specification wording
Meiosis: Students should be able to explain how meiosis halves the number of chromosomes in gametes and fertilisation restores the full number of chromosomes.
Meiosis is a type of cell division that produces gametes with half the normal chromosome number.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 7
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Meiosis is a type of cell division that produces gametes with half the normal chromosome number. A human body cell has 46 chromosomes (23 pairs), but a gamete has 23 single chromosomes. During meiosis, the cell divides twice: the first division separates homologous chromosomes, and the second separates sister chromatids, so four haploid cells form. Because the chromosomes are shuffled and recombined, each gamete is genetically unique. At fertilisation, a male gamete nucleus fuses with a female gamete nucleus, forming a zygote. The two haploid sets combine, restoring the diploid number, so the zygote has 46 chromosomes. This keeps the chromosome number constant across generations and creates genetic variation in the offspring.
What earns the marks
- Meiosis halves the chromosome number, producing haploid gametes.
- In humans, body cells are diploid with 46 chromosomes, while gametes are haploid with 23 chromosomes.
- Meiosis involves two divisions, producing four genetically different haploid cells.
- Fertilisation is the fusion of two gamete nuclei, restoring the diploid chromosome number in the zygote.
- The restoration of the diploid number keeps the chromosome number constant between generations.
Common mistakes and how to put them right
Saying meiosis produces identical cells.
Put it right by stating that meiosis produces genetically different gametes due to recombination and independent assortment.
Confusing haploid and diploid numbers.
Put it right by stating that gametes are haploid (23 in humans) and the zygote is diploid (46 in humans).
Stating that fertilisation doubles the chromosome number permanently.
Put it right by explaining that it restores the diploid number, which stays constant in body cells.
Exam tips
- Use the terms haploid and diploid correctly and give the human chromosome numbers as an example.
- Describe meiosis as two divisions producing four gametes, and fertilisation as the fusion of two gamete nuclei.
- Explain the consequence: the diploid number is restored, so chromosome number stays constant across generations.
Try the lesson
The start of the Meiosis: Students should be able to explain how meiosis halves the number of chromosomes in gametes and fertilisation restores the full number of chromosomes. lesson, made from checked teaching notes for this specification point.
Have a go first
What is the name of the cell division that halves the number of chromosomes to form gametes?
Listen
Meiosis is a type of cell division that produces gametes with half the normal chromosome number. A human body cell has 46 chromosomes (23 pairs), but a gamete has 23 single chromosomes. During meiosis, the cell divides twice: the first division separates homologous chromosomes, and the second separates sister chromatids, so four haploid cells form. Because the chromosomes are shuffled and recombined, each gamete is genetically unique. At fertilisation, a male gamete nucleus fuses with a female gamete nucleus, forming a zygote. The two haploid sets combine, restoring the diploid number, so the zygote has 46 chromosomes. This keeps the chromosome number constant across generations and creates genetic variation in the offspring. A strong answer earns marks for these points. Meiosis halves the chromosome number, producing haploid gametes. In humans, body cells are diploid with 46 chromosomes, while gametes are haploid with 23 chromosomes. Meiosis involves two divisions, producing four genetically different haploid cells. Fertilisation is the fusion of two gamete nuclei, restoring the diploid chromosome number in the zygote. A common slip: Saying meiosis produces identical cells. Instead, stating that meiosis produces genetically different gametes due to recombination and independent assortment. Exam tip: Use the terms haploid and diploid correctly and give the human chromosome numbers as an example.
Key words
Say what each word means before you turn the card.
Gametes
Try answering aloud or in your head before turning the card.
Fertilisation
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See every definition
- Gametes
- These are produced by meiosis and have half the normal chromosome number, such as 23 single chromosomes in humans.
- Fertilisation
- This is the fusion of two gamete nuclei, restoring the diploid chromosome number in the zygote.
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