Q.Explain why meiosis is essential for organisms that reproduce sexually, with reference to the maintenance of a constant chromosome number across generations.

[!TLDR]

Meiosis halves the chromosome number during gamete formation, so fertilisation restores, rather than doubles, the diploid number every generation. …

Sexual reproduction works by the fusion of two gametes, one contributed by each parent, at fertilisation, to form a single zygote. If the gametes themselves carried the full diploid (2n) chromosome number present in the parent's ordinary body cells, then every act of fertilisation would double the chromosome number in the resulting zygote compared with either parent, and this doubling would compound with every successive generation, quickly producing an unworkable, ever-increasing chromosome count. Meiosis prevents exactly this outcome by halving the chromosome number during gamete formation, from diploid (2n) to haploid (n), so that when two haploid gametes fuse at fertilisation, the diploid number is precisely restored in the zygote rather than doubled. It is this halving, performed specifically by meiosis and not by mitosis, that allows the chromosome number characteristic of a sexually re …

Reason through what would go wrong WITHOUT meiosis (doubling every generation) to see why th …

Explaining only that meiosis 'produces haploid gametes' without connecting this to WHY that halving is necessary -- to prevent …