Asexual Reproduction in Single-Celled Organisms

In asexual reproduction, only a single parent is involved in producing offspring. This process does not involve gamete formation or fertilisation. The offsprings are an exact copy of their parents and are termed clones. Clones are genetically and morphologically similar organisms as they inherit all of their chromosomes from one parent. In asexual reproduction, offspring are produced from non-sexual reproductive units like fragments, buds, etc. The process is also called blastogenesis, as blasts are the asexual reproductive body.

Characteristics of Asexual Reproduction

The characteristics of asexual reproduction are as follows:

1. Asexual reproduction is uniparental because it only uses a single parent for offspring production.
2. Gametes are not required for asexual reproduction; therefore, it can occur with or without gamete formation, but fertilisation, i.e., gametic fusion, is absent.
3. The cell division involved in this process is only mitosis.
4. Any unspecialised or specialised part of the parent can lead to asexual reproduction.
5. Organisms that have a relatively simple organisation, like single-celled organisms belonging to group monera, Protista, and plants and animals with a relatively simple organisation like algae, fungi, and sponges, are the common ones that reproduce through asexual mode.
6. The new individual is produced from the somatic cell of the parent; therefore, it is referred to as somatogenic reproduction.
7. The main difference between sexual and asexual reproduction is that the latter does not play any role in evolution. The offspring produced lacks variation as there is no new gene combination.

Advantages of Asexual Reproduction

Here are the advantages of asexual reproduction:

1. The main difference between sexual and asexual reproduction is that there is no requirement for a sexual partner for asexual reproduction.
2. It is a low energy-consuming process because of gamete production.
3. During favourable conditions, many offspring are produced rapidly.
4. The offspring produced by asexual reproduction can quickly adapt to similar environmental conditions because parents and offsprings are identical.

Disadvantages of Asexual Reproduction

Some disadvantages of asexual reproduction include

1. Asexual reproduction lacks gamete union; therefore, there are no chances of new gene combinations, and no variation is found in members of a species. Due to this, the offspring finds it challenging to adapt to changing environmental conditions.
2. Asexual reproduction may lead to overpopulation of a species because it sometimes results in the production of many offspring in one cycle. This large number of offspring produced competes for food resources and space.

Types of Asexual Reproduction

Fission

• It is a form of asexual reproduction in which a fully grown parental organism divides into two or more daughter cells.
• The reproductive unit is the whole parental body in fission. 

Types of Fission

• Binary fission: Here, the parent body divides to give rise to two nearly identical daughter cells. It occurs during favourable conditions. In this process, the mode of reproduction is cell division itself. It is found in many single-celled organisms belonging to the kingdom Monera (Bacteria), Protista, and green algal forms (Chlamydomonas). 
• Multiple fission: This form of asexual reproduction involves dividing the parental body into many daughter cells simultaneously during unfavourable conditions to increase the chances of survival of daughter cells. Many organisms like algae, plasmodium, etc., reproduce by multiple fission. 

Budding

• Budding is a form of asexual reproduction in which the new organisms develop from an outgrowth (bud) from the parent body.
• The formation of the bud-like structure on the parental body is due to repeated cell division.
• Budding is found in yeast, hydra, sponges, etc.
• Unlike binary fission, the parent’s identity, the body, is retained after reproduction. 

Mechanism of Budding

• Initially, the bud-like structure is produced due to repeated mitotic division in the parent body at a particular site.
• The bud continues to grow and enlarges until it acquires parental character.
• Later, the bud constricts at the base and eventually separates from the parent body.
• After detachment of the bud from the parent body, it starts an independent life.
• The bud feeds, becomes an adult, and repeats the process.

Types of Budding

• External budding: In this type, the bud is formed at the outer surface of the parent body and is called exogenous budding. Some examples of this type of asexual reproduction are Hydra and Scypha.

• Internal budding: In this type, the buds are formed inside the parental body and thus are called endogenous budding. In Sponginella, several internal buds are formed endogenously. These internal buds are called gemmules.

Fragmentation

• It is a form of asexual reproduction in which the parental body breaks into two or more fragments, and each piece develops into a new organism.
• The breakage of the parental body into fragments could be either by wave action or death and decay of old parts.
• Fragmentation is seen in flatworms (Microstomum), echinoderms, and spirogyra.

Regeneration

• It is a process in which the damaged part of the body of a living organism shows complete or partial growth.
• Regeneration can be defined as the natural ability to live organisms to replace worn-out parts and repair or renew the complete body.
• There are some organisms in which a complete organism is regenerated from the lost body part.
• Some organisms like planaria, sea urchins, etc., reproduce asexually via regeneration. 

Types of Regeneration 

• Reparative regeneration: Only repair of specific damaged cells of the body. A common phenomenon is observed in both invertebrates as well as vertebrates.
• Restorative regeneration: Organism can redevelop the severed body parts or form the whole body from a body segment. It is very common in invertebrates, e.g., humans and lizards.

Conclusion

Asexual reproduction is a type of reproduction in which the male and female gametes are not involved. Only a single parent undergoes the reproduction process and produces identical copies of the parent. Asexual reproduction is best suited to maintain the true breed of the organism. No genetic diversity is observed in the offspring produced, which means they can easily adapt to harsh environmental conditions. It is the most primitive form of reproduction.