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A-Level Biology October/November 2024 Q5(c): Explain the need for a reduction division during meiosis in the production of gametes i…
A-Level Biology · Paper 9700/41 · October/November 2024 · Question 5(c) · [3 marks]
Explain the need for a reduction division during meiosis in the production of gametes in animals such as horses.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
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Meiosis is a reduction division, which is necessary to halve the chromosome number from diploid (2n) to haploid (n) in the gametes. This ensures that when two gametes fuse during fertilisation, the diploid chromosome number is restored in the resulting zygote. This process is essential to maintain the constant chromosome number for the species from one generation to the next.
Additionally, meiosis introduces genetic variation into the gametes produced. This is achieved through crossing over and independent assortment, leading to variation in the offspring, which is important for adaptation and evolution.
How the marks are awarded
- B1 — Stating that the reduction division is needed to restore the diploid number upon fertilisation, which maintains the chromosome number.
- B1 — Explicitly linking the maintenance of the chromosome number to continuity 'from one generation to the next'.
- B1 — Explaining that meiosis is also needed to introduce genetic variation in the gametes and subsequent offspring.
Common mistakes
- Confusing meiosis with mitosis, or incorrectly stating that meiosis produces diploid cells.
- Simply stating 'to make gametes' without explaining why a reduction in chromosome number is necessary.
- Failing to mention the restoration of the diploid number at fertilisation as the key reason for halving the number in gametes.
- Describing the stages of meiosis in detail instead of explaining its overall purpose and necessity.
Examiner tip: For 'explain the need' questions, always link the biological process to its functional consequence for the organism or for the continuity of the species across generations.
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