meosis.
Genetic diversity of each see. During prophase you get genetic recombination. the single chromosomes of a reproductive cell are all unspindled and mixed up and then bundle back together after they duplicate, but in a somwhat random. So the two resulting ovum or pollen can be drastically different fro each other.
mitosis - normal cellular reprudction that clones
Meosis - sex cell reproduction that creates genetic diversity so we aren't all clones... or plants aren't all clones etc.