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Asexual reproduction occurs in prokaryotic microorganisms (bacteria) and in some eukaryotic single-celled and multi-celled organisms. Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly. Show In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment. In an unstable or unpredictable environment asexually-reproducing species may be at a disadvantage because all the offspring are genetically identical and may not have the genetic variation to survive in new or different conditions. On the other hand, the rapid rates of asexual reproduction may allow for a speedy response to environmental changes if individuals have mutations. An additional advantage of asexual reproduction is that colonization of new habitats may be easier when an individual does not need to find a mate to reproduce. There are a number of ways that animals reproduce asexually. FissionFission, also called binary fission, occurs in prokaryotic microorganisms and in some invertebrate, multi-celled organisms. After a period of growth, an organism splits into two separate organisms. Some unicellular eukaryotic organisms undergo binary fission by mitosis. In other organisms, part of the individual separates and forms a second individual. This process occurs, for example, in many asteroid echinoderms through splitting of the central disk. Some sea anemones and some coral polyps (Figure 1a) also reproduce through fission. BuddingBudding is a form of asexual reproduction that results from the outgrowth of a part of a cell or body region leading to a separation from the original organism into two individuals. Budding occurs commonly in some invertebrate animals such as corals and hydras. In hydras, a bud forms that develops into an adult and breaks away from the main body, as illustrated in Figure 1b, whereas in coral budding, the bud does not detach and multiplies as part of a new colony.  Figure 1. (a) Coral polyps reproduce asexually by fission. (b) Hydra reproduce asexually through budding. (credit a: G. P. Schmahl, NOAA FGBNMS Manager)
Watch a video of a hydra budding. Note that there is no audio in this video. You can view the descriptive transcript for “Budding In Hydra” here (opens in new window). FragmentationFigure 2. Sea stars can reproduce through fragmentation. The large arm, a fragment from another sea star, is developing into a new individual. Fragmentation is the breaking of the body into two parts with subsequent regeneration. If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow. For example, in many sea stars, asexual reproduction is accomplished by fragmentation. Figure 2 illustrates a sea star for which an arm of the individual is broken off and regenerates a new sea star. Fisheries workers have been known to try to kill the sea stars eating their clam or oyster beds by cutting them in half and throwing them back into the ocean. Unfortunately for the workers, the two parts can each regenerate a new half, resulting in twice as many sea stars to prey upon the oysters and clams. Fragmentation also occurs in annelid worms, turbellarians, and poriferans. Note that in fragmentation, there is generally a noticeable difference in the size of the individuals, whereas in fission, two individuals of approximate size are formed. ParthenogenesisParthenogenesis is a form of asexual reproduction where an egg develops into a complete individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process and the species. Parthenogenesis occurs in invertebrates such as water flees, rotifers, aphids, stick insects, some ants, wasps, and bees. Bees use parthenogenesis to produce haploid males (drones) and diploid females (workers). If an egg is fertilized, a queen is produced. The queen bee controls the reproduction of the hive bees to regulate the type of bee produced. Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Although more common in plants, parthenogenesis has been observed in animal species that were segregated by sex in terrestrial or marine zoos. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males. Contribute!Did you have an idea for improving this content? We’d love your input. Improve this pageLearn More
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Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is known as a bud. Since the reproduction is asexual, the newly created organism is a clone and excepting mutations is genetically identical to the parent organism. Organisms such as hydra use regenerative cells for reproduction in the process of budding. In hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and, when fully mature, detach from the parent body and become new independent individuals. Internal budding or endodyogeny is a process of asexual reproduction, favored by parasites such as Toxoplasma gondii. It involves an unusual process in which two daughter cells are produced inside a mother cell, which is then consumed by the offspring prior to their separation.[1] Endopolygeny is the division into several organisms at once by internal budding. Cellular reproductionSome cells divide asymmetrically by budding, for example Saccharomyces cerevisiae, the yeast species used in baking and brewing. This process results in a 'mother' cell and a smaller 'daughter' cell. Cryo-electron tomography recently revealed that mitochondria in cells divide by budding. Animal reproductionIn some multicellular animals, offspring may develop as outgrowths of the mother. Animals that reproduce by budding include corals, some sponges, some acoels (e.g., Convolutriloba), and echinoderm larvae. Colony divisionColonies of some bee species have also exhibited budding behavior, such as Apis dorsata. Although budding behavior is rare in this bee species, it has been observed when a group of workers leave the natal nest and construct a new nest usually near the natal one.[2] VirologyIn virology, budding is a form of viral shedding by which enveloped viruses acquire their external envelope from the host cell membrane, which bulges outwards and encloses the virion. Plant multiplicationIn agriculture and horticulture, budding refers to grafting the bud of one plant onto another. See also
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What method of asexual reproduction is the separation division of an organism to form individuals of approximately same size?
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