The process by which cells and organisms produce other cells and organisms of the same kind. ♦ The reproduction of organisms by the union of male and female reproductive cells (gametes) is called sexual reproduction. Many unicellular and most multicellular organisms reproduce sexually. ♦ Reproduction in which offspring are produced by a single parent, without the union of reproductive cells, is called asexual reproduction. The fission (splitting) of bacterial cells and the cells of multicellular organisms by mitosis is a form of asexual reproduction, as is the budding of yeast cells and the generation of clones by runners in plants. Many plants and fungi are capable of reproducing both sexually and asexually, as are some animals, such as sponges and aphids.