Asexual reproduction occurs when an organism makes more of itself without exchanging genetic information with another organism through sex. In sexually reproducing organisms, the genomes of two parents are combined to create offspring with unique genetic profiles. This is beneficial to the population because genetically diverse populations have higher chance of withstanding survival challenges such as disease and environmental changes.
Asexually reproducing organisms can suffer a dangerous lack of diversity — but they can also reproduce faster than sexually reproducing organisms, and a single individual can found a new population without the need for a mate. Some organisms that practice asexual reproduction can exchange genetic information to promote diversity using forms of horizontal gene transfer such as bacteria who use plasmids to pass around small bits of DNA.
However this method results in fewer unique genotypes than sexual reproduction. Some species of plants, animals, and fungi are capable of both sexual and asexual reproduction, depending on the demands of the environment. Asexual reproduction is practiced by most single-celled organisms including bacteria, archaebacteriaand protists.
Puoliautomaattinen asexual reproduction is also practiced by some plants, animals, and fungi. This is especially useful for species whose survival strategy is to reproduce very fast. Many species of bacteria, for example, can completely rebuild a population from just a single mutant individual in a matter of days if most members Puoliautomaattinen asexual reproduction wiped out by a virus. This is useful for species whose Puoliautomaattinen asexual reproduction may find themselves isolated, such as fungi that grow from wind-blown spores, plants that rely on pollinators for sexual reproduction, and animals inhabiting environments with low population density.
Asexual reproduction, which can often be accomplished just by having part of the parent organism split off and Puoliautomaattinen asexual reproduction on a life of its own, takes fewer resources than nurturing a new baby organism. Many plants and sea creatures, for example, can simply cut a part of themselves off from the parent organism and have that part survive on its own. Only offspring that are genetically identical to the parent can be produced in this way: This ability to simply split in two is one reason why asexual reproduction is faster than sexual reproduction.
The biggest disadvantage of asexual reproduction is lack of diversity. Because members of an asexually reproducing population are genetically identical Puoliautomaattinen asexual reproduction for rare mutants, they are all Puoliautomaattinen asexual reproduction to the same diseases, nutrition deficits, and other types of environmental hardships. The Irish Potato Famine was one example of the down side of asexual reproduction: As a result, almost all crops failed, and many people starved.
The near-extinction of the Gros-Michel banana is another example — one of two major cultivars of bananas, it became impossible to grow commercially in the 20th century after the emergence of a disease to which it was genetically vulnerable. On the other hand, many species of bacteria actually take advantage of their high mutation rate to create some genetic diversity while using asexual reproduction to grow their colonies very rapidly.
Bacteria have a higher rate of errors in copying genetic sequences, which sometimes leads to the creation of Puoliautomaattinen asexual reproduction new traits even in the absence of sexual reproduction. Some organisms split off a small part of themselves to grow into a new organism. This is practiced by many plants and sea creatures, and some single-celled eukaryotes such as yeast.
Much like budding, this process involves a plant growing a new shoot which is capable of becoming a whole new organism. Sporogenesis is the production of reproductive cells, called spores, which can grow into a new organism.
Spores often use similar strategies to those of seeds. But unlike seeds, spores can be created without fertilization by a sexual partner. Spores are also more likely to spread autonomously, such as via wind, than to rely on other organisms such as animal carriers to spread.
This process resembles budding and vegetative propagation, but with some Puoliautomaattinen asexual reproduction.
Earthworms and many plants and sea creatures are capable of regenerating whole organisms from fragments following injuries that split them Puoliautomaattinen asexual reproduction multiple pieces. When fragmentation does occur voluntarily, the same parent organism may split into many roughly equal parts in order to form many offspring. This is different from the processes of budding and vegetative propagation, where an organism grows new parts which are small compared to the parent and which are intended to become offspring organisms.
Agamenogenesis is the reproduction of normally sexual organisms without the need for fertilization. There are several ways in which this can happen. In parthenogenesis, an unfertilized egg begins to develop into a new organism, which by necessity possesses only genes from its mother.
This occurs in a few species of all-female animals, and in females of some animal species when there are no males present to fertilize eggs. In apomoxis, a normally sexually reproducing plant reproduces asexually, offspring that are identical to the parent plant, due to lack of availability of a male plant to fertilize female gametes. This is primarily known to occur in fruit, which may produce seeds in this way in the absence of male fertilization.
Because they have only one cell, bacteria are able to change their genetic material as mature organisms. Bacteria can afford to Puoliautomaattinen asexual reproduction this survival strategy because their extremely rapid reproduction makes harmful genetic mutations — such as copying errors or horizontal gene transfer gone wrong — inconsequential to the whole population.
As long as a few individuals survive mutation and calamity, those individuals will be able to rebuild the bacterial population quickly. This strategy would not work well for an organism that invests highly in the survival of individuals, such as multicellular organisms. Slime molds are a fascinating organism that sometimes behave like a multicellular organism, and sometimes behave like a colony of "Puoliautomaattinen asexual reproduction" organisms.
Unlike animals, plants, and fungi, the cells in a slime mold are not bound together in a fixed shape and dependent on each other for survival. The cells that make up a slime mold are capable of living individually and may spread or separate when food is abundant, much like individuals in a colony of bacteria.
Slime molds whose cells are working cooperatively can be mistaken for fungi, and can perform locomotion.