In asexual reproduction, one individual produces offspring that are genetically identical to itself. Reproduction is a marvelous culmination of individual transcendence in that organisms "transcend" time through the reproduction of offspring. In animal organisms, reproduction can occur by two primary processes: asexual reproduction and sexual reproduction.
Organisms produced by asexual reproduction are the product of mitosis. In this process, a single parent replicates body cells and divides into two individuals. Many invertebrates, including sea stars and sea anemones, reproduce in this manner. Common forms of asexual reproduction include: budding, gemmules, fragmentation, regeneration, binary fission, and parthenogenesis.
Many hydras reproduce asexually by producing buds in the body wall, which grow to be miniature adults and break away when they are mature. Ed Reschke/Photolibrary/Getty Images
Hydras exhibit a form of asexual reproduction called budding. In this form of asexual reproduction, an offspring grows out of the body of the parent, then breaks off into a new individual. In most instances, the budding is restricted to certain specialized areas. In some other limited cases, buds may come from any number of places on the body of the parent. The offspring typically remain attached to the parent until it is mature.
Progeny are budding on the body of a sponge in the Red Sea. Jeff Rotman Photography/Corbis Documentary/Getty Images
Sponges exhibit a form of asexual reproduction that relies on the production of gemmules or internal buds. In this form of asexual reproduction, a parent releases a specialized mass of cells that can develop into offspring. These gemmules are hardy and can be formed when the parent experiences harsh environmental conditions. The gemmules are less likely to become dehydrated and in some cases may be able to survive with a limited oxygen supply.
Planaria can reproduce asexually by fragmentation. They split into fragments, which develop into adult planaria. Ed Reschke/Photolibrary/Getty Images
Planarians exhibit a form of asexual reproduction known as fragmentation. In this type of reproduction, the body of the parent breaks into distinct pieces, each of which can produce an offspring. The detachment of the parts is intentional, and if thy are large enough, the detached parts will develop into new individuals.
Starfish are able to regrow missing limbs and produce new organisms through regeneration. Paul Kay/Oxford Scientific/Getty Images
Echinoderms exhibit a form of asexual reproduction known as regeneration. In this form of asexual reproduction, a new individual develops from a part of another. This typically happens when a part, like an arm, becomes detached from the parent's body. The separated piece can grow and develop into a completely new individual. Regeneration can be thought of as a modified form of fragmentation.
This paramecium is dividing by binary fission. Ed Reschke/Photolibrary/Getty Images
Paramecia and other protozoan protists, including amoebae and euglena, reproduce by binary fission. In this process, the parent cell duplicates its organelles and increases in size by mitosis. The cell then divides into two identical daughter cells. Binary fission is typically the most common form of reproduction in prokaryotic organisms such as bacteria and archaea.
This water flea (Daphnia longispina) can be seen with developing parthenogenetic or unfertilized eggs.
Roland Birke/Photolibrary/Getty Images
Parthenogenesis involves the development of an egg that has not been fertilized into an individual. Most organisms that reproduce through this method can also reproduce sexually. Animals like water fleas reproduce by parthenogenesis. Most kinds of wasps, bees, and ants (which have no sex chromosomes) also reproduce by parthenogenesis. Additionally, some reptiles and fish are capable of reproducing in this manner.
This sea star has lost an arm which can develop into a new sea star by the asexual process of fragmentation.
Karen Gowlett-Holmes/Oxford Scientific/Getty Images
Asexual reproduction can be very advantageous to certain higher animals and protists. Organisms that remain in one particular place and are unable to look for mates would need to reproduce asexually. Another advantage of asexual reproduction is that numerous offspring can be produced without "costing" the parent a great amount of energy or time. Environments that are stable and experience very little change are the best places for organisms that reproduce asexually.
One major disadvantage of this type of reproduction is the lack of genetic variation. All of the organisms are genetically identical and therefore share the same weaknesses. A gene mutation can persist in the population as it is continuously repeated in the identical offspring. Since organisms produced asexually grow best in a stable environment, negative changes in the environment can have deadly consequences for all individuals. Due to the high numbers of offspring that can be produced in a relatively short period of time, population explosions often occur in favorable environments. This extreme growth may lead to rapid depletion of resources and an exponential death rate in the population.
This is a colored scanning electron micrograph (SEM) of puffball fungus spores. These are the reproductive cells of the fungus. Credit: Steve Gschmeissner/Science Photo Library/Getty Images
Animals and protists are not the only organisms that reproduce asexually. Yeast, fungi, plants, and bacteria are capable of asexual reproduction as well. Yeast reproduce most commonly by budding. Fungi and plants reproduce asexually through spores. Plants can also reproduce by the asexual process of vegetative propagation. Bacterial asexual reproduction most commonly occurs by binary fission. Since the bacterial cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics.
Form of cellular asexual reproduction
This article is about the form of asexual reproduction. For other uses, see Budding (disambiguation).
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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 reproduction
Some 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 reproduction
In 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 division
Colonies 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]
Virology
In 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 multiplication
See also: Shield budding, Vegetative reproduction, and Chip budding
In agriculture and horticulture, budding refers to grafting the bud of one plant onto another.
See also
- Fragmentation (reproduction)
- Paratomy
- Fission (biology)
- Strobilation
References
- ^ James Desmond Smyth, Derek Wakelin (1994). Introduction to animal parasitology (3 ed.). Cambridge University Press. pp. 101–102. ISBN 0-521-42811-4.
- ^ Oldroyd, B.P. (2000). "Colony relatedness in aggregations of Apis dorsata Fabricius (Hymenoptera, Apidae)". Insectes Sociaux. 47 (47): 94–95. doi:10.1007/s000400050015. S2CID 40346464.
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