There are two ways of reproduction of organisms - sexual and asexual reproduction. In the first case, gametes merge, and in the second, development from a somatic cell. When the offspring is reproduced with the participation of a single non-gamete (asexual) individual, a plant or animal born into the world inherits the genes of one parent, and therefore, in the absence of a mutation, it will be an exact copy of it.
Reproduction involving a single parent is different from reproduction, which involves two individuals. The following features of asexual reproduction are distinguished:
Single parent playback process
a multicellular or unicellular organism reproduces and develops with the help of mitosis;
in this process, meiosis is absent;
the number of offspring is increasing rapidly.
All organisms with one cell reproduce asexually, be it fungi, many plant species or multicellular protozoa. This type of reproduction existed long before sexual reproduction.
There are transitional forms from asexual reproduction to sexual reproduction:
parthenogenesis - an individual is formed from the mother's gamete;
hermaphroditism - the only organism has the characteristics of both sexes.
There are several forms of asexual reproduction. The table shows the following types and their features:
Division. Multiple daughter cells are reproduced from a single parental cell as a result of division. There may be more than a thousand of them. Binary fission occurs in prokaryotes. This type of asexual reproduction is a characteristic feature of bacteria, chlorella, amoebas.
Spore formation. There are special organs - sporangia, from which spores are released. The latter have a reliable shell, but it collapses under favorable factors for development. Representatives of wildlife that reproduce by spores are algae, ferns, mushrooms and mosses.
Budding. The offspring is produced from parent tissue as a result of protrusion and separation. An example is hydra.
Fragmentation. A new living organism emerges from a separate part or segments of the parent body. Examples in the surrounding world are coelenterates, tapeworms, algae.
Vegetative reproduction. Unlike other methods of reproduction, offspring is produced from the vegetative organs of plants in a natural or artificial way. This property is typical for the following biological representatives: begonia, violet, geranium. Interestingly, vegetative propagation can be very diverse. In some species, this is possible with the help of whiskers (shoots creeping along the ground).
A person is able to obtain a living organism by an asexual method, artificially. This process is called cloning. In living nature, such a phenomenon occurs extremely rarely. The pattern of true cloning in biology is homozygous, or identical twins. However, they are similar only in comparison with each other and are very different from the parent individuals.
In the modern world, even the cloning of those individuals that are capable of reproducing offspring sexually is capable of being carried out. A simple example is the famous Dolly the sheep. Its cloning was carried out by transferring the nucleus of the somatic cell of the parent to the donor egg. In fact, any type of asexual reproduction will belong to cloning, since the procedure involves a somatic cell instead of a reproductive one, and the new organism is identical to the parent.
As for plants, in test tubes, flasks and Petri dishes, a person receives cells similar to the original specimens. This scheme is based on the totipotency of cells. This property implies the ability of a cell to divide and produce cellular organisms. This phenomenon has many benefits for humans. You can take any part of the plant, be it a root or a stem, place it in the necessary environment, and under favorable conditions, a new copy can be obtained from the base.
However, it is clear that if you take a part of a human body and place it in a special environment, a new individual will not appear. Creating a clone of an animal or human is an extremely complex procedure. Clonal micropropagation has the highest reproductive rate. Due to vegetative propagation, 10-100 plants can appear in one year, clonal micropropagation allows producing from 5 thousand to 1 million units per year. in the laboratory.
It is extremely beneficial to create clones of plants when breeding elite plants, of which there were only a few copies around the world. In the USA, Holland, Belgium, Denmark and Poland there are firms that specialize in plant cloning.
The value of mitosis
The role of mitosis is extremely important. Thanks to him, the required set of chromosomes is maintained. An identical cell can only be produced using this method.
It is according to this principle that the cells of the epidermis and intestinal epithelium are renewed. There is a copying, which means the preservation of the genetic code.
Using this method, it is possible to restore body parts in certain classes of organisms, for example, rays from a starfish. Mitosis provides asexual reproduction, for example, vegetative reproduction of plants and budding in hydras. Mitosis differs from meiosis in the duration of the phases and the peculiarities of the processes occurring in them.
Asexual reproduction is significantly different from same-sex reproduction. The first method does not imply the presence of gametes at all. In parthenogenesis (same-sex reproduction), daughter cells are formed from the mother's egg. As for asexual reproduction, division is characteristic of unicellular organisms, and budding, vegetative reproduction, fragmentation, and sporulation are characteristic of multicellular organisms. Asexual reproduction occurs in unicellular fungi, animals and plants. This process takes a little time and allows you to increase the number of the species in a short time.