Types of Asexual Reproduction

Reproduction is one of the most important concepts in science. Reproduction involves developing a copy of an individual and therefore ensuring the survival of a species. Although reproduction is frequently thought of in terms of the creation of offspring in animals and plants, it has a far greater scope for living entities. The genesis of life and the evolution of organisms must also be considered. The ability to produce primitive organisms by duplicating itself is the first trait in prehistoric times.

Asexual and sexual reproduction are the two ways an organism can reproduce. However, there are various types involved in both ways. Asexual reproduction is a mode of reproduction that does not include germ cells fusion or chromosomal number changes. Offspring produced through asexual reproduction is from either unicellular or multicellular organisms that acquire the entire set of genes of their single parent. Offspring are produced at a higher rate in asexual beings as it does not involve waiting for a partner.

Types of asexual reproduction

The different types of asexual reproduction are fission, budding, vegetative propagation, spore formation, fragmentation, parthenogenesis, and apomixis.

Fission

 It is that type of asexual reproduction in which a fully grown parental organism divides into two or more than two daughter cells. In this, the reproductive unit is the whole parental body. Types of Fission: Based on several daughter cells produced, fission is of two types:

 (a)    Binary fission and    (b) Multiple fission.

Binary fission

Binary fission is a type of asexual reproduction wherein a cell divides itself to produce two identical cells called clones. Each of these two cells has the potential to grow to the size of the original cell. Organisms that reproduce by binary fission are predominantly bacteria.

Types: Based on the plane of cytokinesis, binary fission is of three types:

 (a)    Irregular or simple binary fission: Here cytokinesis may take place along any plane but its plane is always perpendicular to that of karyokinesis e.g., Amoeba.

 (b)  Longitudinal binary fission: Here cytokinesis takes place along the longitudinal axis e.g., in flagellates (Euglena).

 (c)  Transverse binary fission: Here cytokinesis takes place along the transverse axis e.g., in ciliated protozoans (Paramedium).

Multiple fission

 It is that type of asexual reproduction in which the parental body divides into many daughter cells simultaneously during the unfavourable conditions to increase the chances of survival of daughter cells. In this, the reproductive unit is the whole parental body. E.g., algae among plants, Plasmodium malarial parasite, Amoeba, and Monocytes.

Budding

Budding is a type of asexual reproduction that involves the formation of an outgrowth, called a bud, from the body of an organism. This bud has a special ability to develop into a new individual that is identical to the parent organism. It may stay attached to the organism or cut off from the parent. Fungi, hydra, and flatworms reproduce in this manner.

Vegetative propagation

Vegetative propagation takes place in plants. It occurs from the vegetative part of the plant, which means those parts of a plant that does not involve gametes, such as leaves, stems, and roots. This type of reproduction occurs in two ways, natural way, and artificial way. Examples of natural means are strawberries emerge from runners (stolon). 

Spore formation (sporogenesis)

As the name suggests, this mode of reproduction involves the production of spores. The word ‘spore’ is derived from ‘seed’. Spores are dormant cells that can reproduce when dispersed. However, these do not contain embryo formation by the gamete fusion. Spores are highly resistant to changing temperatures and humidity. When a favourable temperature occurs, spores germinate to give rise to new individuals. Vascular plants are examples of spore formation. 

Fragmentation

Fragmentation is the process of the formation of pieces of a parent organism. Each piece of the parent can develop into a whole new individual. Formation of pieces of parent organism is not done on purpose. However, human activity and other environmental factors caused them to break into fragments. Such a process is widely observed in yeasts and cyanobacteria. Planaria is the best example of fragmentation.

Parthenogenesis

Parthenogenesis is an asexual reproduction that involves only a female parent of the organism. It does not involve fertilisation with the male counterpart. This further involves two processes: apomictic and automictic. Apomictic is a process in which egg cells are produced by mitosis and mature directly into embryos, whereas automictic parthenogenesis involves cells undergoing meiosis and forms a mature egg cell. Examples include lizards.

Plant apomixis

To understand apomixis, we should understand what sporophytes and gametophytes are. A sporophyte is a generation in a plant (diploid) that involves the production of haploid spores. A gametophyte is a generation of plants that involves the production of gametes followed by the fusion resulting in the zygote.

Apomixis is a type of asexual reproduction in plants that do not involve fertilisation. In certain plants, like ferns, the gametophyte produces a sporophyte-looking offspring with the same ploidy as the gametophyte. This is referred to as apogamy. In some other plants, a sporophyte produces a gametophyte-looking offspring with a ploidy level of a sporophyte. This process is called apospory.

Advantages of asexual reproduction

• The number of offspring produced is high.
• There is no involvement of two parents, as asexual reproduction involves a single parent.
• Since it involves single parents, the energy requirement is less.
• It helps in conserving species’ genetic material.
• There are multiple ways in which asexual reproduction can take place.

Conclusion

Reproduction, sexual or asexual, plays a vital role in our existence on the planet and continuing life. The sexual mode of reproduction involves genetic diversity as it involves the fusion of germ cells from both parents and thus helps in surviving the organism in critical conditions, while asexual reproduction helps to conserve the pure breed of the species on the planet. As many organisms are constantly reproducing and adapting to new environments, it is important to be a part of the living system. If the organism does not divide and reproduce, its survival and existence will be difficult and finally will be eliminated from the planet, thus creating an imbalance in the ecosystem.