Science (086) — AI-generated practice question

During sexual reproduction, each parent produces gametes (sperm or egg) through a process where chromosome pairs separate, so each gamete carries only one chromosome from each pair. When two gametes fuse at fertilisation, the resulting offspring receives one chromosome from each parent, restoring the full chromosome number (46 in humans = 22 pairs + sex chromosomes). This ensures the chromosome number remains constant across every generation.

Genetic variation arises because:

• Each offspring receives a unique combination of chromosomes from both parents.
• Sexually reproducing individuals have two copies of each gene; these may differ (dominant/recessive), producing varied traits.
• Traits can be inherited independently, giving rise to new combinations in offspring.

Thus, sexual reproduction both maintains chromosomal stability and maximises variation, which may improve survival of the species.

Source: Chapter 8 — Heredity; Chapter 7 — What you have learnt

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What examiners look for (5 marks):

1. (~1 mark) Gametes carry one chromosome from each pair (halving).
2. (~1 mark) Fertilisation restores the full chromosome number — this is the key mechanism for preservation.
3. (~1 mark) Unique chromosome combinations from two parents → variation.
4. (~1 mark) Dominant/recessive gene pairs contribute to variation.
5. (~1 mark) Independent inheritance of traits → new trait combinations.

Key tip: Always explicitly link halving in gametes + fusion at fertilisation = constant chromosome number. Many students explain variation well but forget to clearly state the restoration mechanism — that's where marks are lost.