For the biological diversity is mitosis or meiosis the more important process?
Meiosis is the cell division process that permits the formation of gametes to sexual reproduction, with aleatory separation of every chromosome of the individual homologous pairs. These gametes can fecundate gametes from other individuals promoting combination of homologous chromosomes from dissimilar individuals. In that manner the chromosomal recombination given by meiosis and sexual reproduction makes individuals with dissimilar genetic patrimony from their fathers and thus promotes biological diversity.
Some fungi species and plants, for instance, present sporic meiosis, i.e., a structure where half of the chromosomes of the species is formed from meiosis. This structure, by mitosis, forms gametes. Even in this case diversity comes from meiosis. Meiosis then is the cell division process that in conjunction with genetic mutations is responsible for the biological diversity.