Significance of Meiosis

Meiosis serves three closely related biological purposes. First, it maintains a constant, definite chromosome number across generations of a sexually reproducing species: because meiosis halves the chromosome number when gametes are formed, the subsequent fusion of two haploid gametes at fertilisation restores exactly the diploid number characteristic of the species, generation after generation - without this halving step, chromosome number would double every generation. Second, meiosis generates genetic variation: crossing over during prophase I exchanges genetic material between non-sister chromatids of homologous chromosomes, and independent assortment during metaphase I and anaphase I randomly distributes different combinations of maternal and paternal chromosomes into the resulting gametes; together these two mechanisms mean no two gametes (and, in practice, no two offspring) are genetically identical. These variations are far from trivial - they are the raw material on which natural selection acts, making meiosis a key driver of evolution. Third, by continually generating this variation, meiosis improves a population's capacity to adapt to ch …