Asexual reproduction is a mode of reproduction in which the new offspring are produced from a single parent. The offspring produced are identical to each other, both physically as well as genetically. They are the exact copies of their parent cell. Hence, they are called clones. Asexual reproduction is observed in both unicellular and multicellular organisms.
Features of Asexual Reproduction
- Single parent involved
- No gamete formation or fertilization
- The whole process takes place in a small period of time
- Rapid multiplication and growth
- Limited variation (genetically similar)
Modes of Asexual Reproduction
Organisms choose to reproduce asexually by different means. Some of the asexual methods are binary fission (e.g. Amoeba, bacteria), budding (e.g. Hydra), fragmentation (e.g. Planaria), spore formation (e.g. ferns) and vegetative propagation (e.g. Onion).
Fission means division. During asexual reproduction, the parent cell divides into two or more cells. Unicellular organisms show different patterns of cell division according to their cell structure i.e., some are directional while others are non-directional. For example, amoeba can divide itself into two at any plane but the division in euglena is longitudinal. Fission can be of two types, namely, binary fission and multiple fission.
In binary fission, parent cell divides into two equal halves called daughter cells. Daughter cells are identical to each other and to their parent cell. Organisms like amoeba, bacteria, euglena, etc., exhibit binary fission.
During multiple fission, organism divides itself into numerous daughter cells.
Fragmentation is another mode of asexual reproduction. Multi-cellular organisms like planaria, spirogyra, etc. reproduce by fragmentation. The parent body divides into two or more fragments. Later, each fragment develops into a new individual.
When a lizard loses its tail, it grows a new one. This is called regeneration. In many organisms, there are specialized cells, which can differentiate and grow into a new organism. Organisms like hydra and planaria also show regeneration. In these organisms, when the cell divides into numerous pieces, each piece proliferates and differentiates to regenerate new organisms.
Some organisms develop buds on their body. These buds develop into a new individual. This is called budding. An example is a hydra. From the parent hydra, a bud arises which eventually matures into a new hydra. Once it is matured, it detaches from the parent body.
Plants reproduce asexually through their vegetative parts such as leaves, roots, stem, and buds. This is called vegetative propagation. For example, onion bulbs, tubers of potato, runners/stolon, etc.
Vegetative propagation is much faster than the sexual reproduction in plants. This can be done artificially as well, which is widely employed in horticulture.Spore formation
Spore formation is another means of asexual reproduction. Organisms which belong to the fungi group produce spores within a sac-like structure called sporangium. Under the favorable condition, sporangium burst to release spores which germinate to form new offspring.
In asexual reproduction, a single cell is divided to produce offspring. Simple cell-by-cell division is not possible in multicellular organisms . Most of the multicellular organisms have a complex body design. They have a higher level of organization like tissues, organs and organ system. Thus, they need a special mode for reproduction.
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