Explain why meiosis is important in sexual reproduction, and describe what happens to chromosomes during meiosis.

Meiosis is the process that generates the sex cells (gametes) used in sexual reproduction. It ensures that each gamete contains only half the chromosome number of a body cell, so that when two gametes fuse during fertilisation the resulting zygote has the normal diploid chromosome number.

During interphase before meiosis, the chromosomes are duplicated so that each chromosome consists of two identical sister chromatids. Meiosis then proceeds through two successive divisions. In meiosis I, homologous chromosomes are separated, producing two cells each with half the chromosome number but still diploid for each chromosome. In meiosis II, the sister chromatids are separated, giving a total of four haploid daughter cells. These four gametes are genetically unique because of crossing‑over and independent assortment.

When fertilisation occurs, the haploid sperm and egg fuse, restoring the diploid chromosome number and forming a zygote that can develop into a new individual.