During sexual reproduction, germ cells undergo meiosis, producing gametes with half the number of chromosomes. When two gametes combine during fertilisation, the original chromosome number is re-established in the new generation. This maintains the DNA content and body design features of the species, ensuring its stability.
Source: Chapter 7, Section 7.3.1 – Why the Sexual Mode of Reproduction?
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The examiner expects two key points for 2 marks:
Avoid writing about variation here — the question is specifically about stability, not variation. Quoting "re-establishment of the number of chromosomes and the DNA content" directly from the textbook is ideal.