Asexual Reproduction

Rubus Berry Plants

Asexual Reproduction

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Rubus Berry Plants

Rubus Berry Plants

Asexual Reproduction

Asexual Reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which refers to reproduction without the fusion of gametes. Asexual reproduction is the primary form of reproduction for single-celled organisms such as the archaea, bacteria, and protists. Many plants and fungi reproduce asexually as well. While all prokaryotes reproduce asexually (without the formation and fusion of gametes), mechanisms for lateral gene transfer such as conjugation, transformation and transduction are sometimes likened to sexual reproduction. A lack of Sexual Reproduction is relatively rare among multicellular organisms, for reasons that are not completely understood. Current hypotheses suggest that Asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments.

Types of asexual reproduction

Binary fission

In binary fission the parent organism is replaced by two daughter organisms, because it literally divides in two. Many single-celled organisms, both prokaryotes (the archaea and the bacteria), and eukaryotes (such as protists and unicellular fungi), reproduce asexually through binary fission; most of these are also capable of sexual reproduction. Some single-celled organisms rely on one or more host Organism in order to reproduce.

Fragmentation

Fragmentation is a form of Asexual reproduction where a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. Fragmentation is seen in many organisms such as animals (some annelid worms and sea stars), fungi, and plants. Some plants have specialized structures for reproduction via fragmentation, such as gemmae in liverworts. Most lichens, which are a symbiotic union of a fungus and photosynthetic algae or bacteria, reproduce through fragmentation to ensure that new individuals contain both symbionts. These fragments can take the form of soredia, dust-like particles consisting of fungal hyphae wrapped around photobiont cells.

Alternation between sexual and asexual reproduction

Some Species alternate between the sexual and asexual strategies, an ability known as heterogamy, depending on conditions. For example, the freshwater crustacean Daphnia reproduces by parthenogenesis in the spring to rapidly populate ponds, then switches to sexual reproduction as the intensity of competition and predation increases. Many protists and fungi alternate between sexual and Asexual reproduction.

For example, the slime mold Dictyostelium undergoes binary fission (mitosis) as single-celled amoebae under favorable conditions. However, when conditions turn unfavorable, the cells aggregate and follow one of two different developmental pathways, depending on conditions. In the social pathway, they form a multicellular slug which then forms a fruiting body with asexually generated spores. In the sexual pathway, two cells fuse to form a giant cell that develops into a large cyst. When this macrocyst germinates, it releases hundreds of amoebic cells that are the product of meiotic recombination between the original two cells.

The hyphae of the common mold (Rhizopus) are capable of producing both mitotic as well as meiotic spores. Many algae similarly switch between sexual and Asexual reproduction. A number of plants use both sexual and asexual means to produce new plants, some species alter there primary mode of reproduction from sexual to asexual under varying environmental conditions.

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