Independent assortment occurs during the metaphase I of meiosis. This is the stage where homologous chromosomes align at the equatorial plate of the cell before they are separated into daughter cells.
During metaphase I, pairs of homologous chromosomes, each consisting of two sister chromatids, line up next to each other. This positioning is crucial because it determines how the chromosomes will segregate into the gametes. Each pair of chromosomes is aligned independently of the others, which means that the distribution of maternal and paternal chromosomes into the daughter cells is random. This randomness leads to genetic variation in the offspring, a key feature of sexual reproduction.
Thus, it is the independent assortment of these chromosomes during metaphase I that contributes significantly to the genetic diversity seen in sexually reproducing populations.