Asexual reproduction

Reproduction is the most essential biological process in any organism. It is defined as the production of offspring by a sexual or asexual process. Reproduction is alternatively used with the terms procreation or breeding, however, these are context-specific terms used narrowly. Reproduction is essentially a need for every organism. The phenomenon is closely connected with the growth and evolution of the entire species. Reproduction is a unique phenomenon which is evidently different from one organism to another, for example, humans take a long course of 9 months 7 days while some fishes finish off the process in a few days, whereas some bacteria gets multiplied between 4 to 20 minutes. Reproduction is not a selective process as organisms cannot determine their type of reproduction, which is why it is one of the areas in Biology requiring extensive research.

 

Types of reproduction

Sexual reproduction requires the fusion between the male and female gametes through sexual contact while Asexual reproduction certainly doesn't require sexual contact between the 2 parents. Hence, asexual reproduction can also happen in laboratory settings through cloning. Asexual reproduction designs a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The primary objective of the reproduction is to achieve the proper transmission of traits from parents to progeny. Plants and animals use different techniques for the transmission of traits from one generation to the other. Most of the animals undergo Sexual reproduction, which can produce a substantial degree of variation between the 2 generations. Sexual reproduction necessitates germ level changes or interventions. The influence of such changes sequentially migrates into every individual cell starting from the 2 fused cells( ovum and sperm). Adding to this, a long course of fertilization is significantly associated with a number of changes in the dividing cells at every moment.  Consequently, by the time a progeny is born, there is a great chance of variation. But this is not the case in asexual reproduction as it nither requires pregnancy nor the extensive cell division in a developing progeny therefore, variations are proportionately lower in the asexually reproduced organisms. Sexual reproduction is a very important aspect of evolution as it improves the fitness and the survival skills of the resulting species by accumulating the variations through each generation, but this is not the case in asexual reproduction. So, the asexually reproduced breeds are less likely to experience variations.

 

 

 

Asexual reproduction

No one is clear why do some organisms reproduce asexually while others sexually. Asexual reproduction does not involve the fusion of gametes or exchange of a number of chromosomes. Rather, offsprings are formed from a single cell or from a multicellular organism through a simple bifurcation of a parent cell into many pieces without sexual contact. Asexual reproduction is the principal method of reproduction in most of the single-celled organisms like archaea and bacteria. Still, some multicellular animals, plants and fungi can also reproduce asexually. Sexual reproduction is highly favoured as a means to carry out proper genetic recombination through conjugation, transformation and transduction. Conversely, asexual reproduction is not a favourable reproduction from the evolution point of view as the mechanism do not necessarily involve a complex way of genetic recombination.

 

Advantages of Asexual Reproduction

1. It is a quick and rapid mode of reproduction that can produce an enormous number of offsprings, however, very few of them survive. This type of phenomenon is observed in some bacterial colonies.

2. Asexual reproduction is relatively easy and simple as it doesn't require the physical contact between 2 organisms.

3. They form a highly homozygous species when compared to those born out of sexual reproduction.

4. Asexual reproduction can transfer positive genetic influences through generations as there is a lesser chance of manipulation in the middle.

 

Disadvantages of Asexual Reproduction

1. Asexual reproduction results in a progeny that look like a photocopy of its parent allowing lesser chances to produce a variation.

2. Asexually reproduced species exhibit poor adaptations skill as they lack stability among its members. Thus, the resulting species are vulnerable for many diseases including malnutrition. One of the best examples is the Irish Potato Famine in which late blight destroyed the leaves and edible roots of the potato plants in a very short span of 4 years.

3. Asexually reproduced unicellular organisms some times born with many genetic errors due to the wrong copying mechanism of the genetic sequences during the reproduction. 

4. The pace of replication during the asexual reproduction is uncontrolled, hence there is a possibility of faulty production of progeny.

 

Differences between sexual and asexual reproduction

Asexual reproduction

Sexual reproduction  

Parent cell involvement

There is no need for fusion between the father and mother.

It necessitates the fusion between two matured opposite genders.

Types of reproduction

Vegetation, binary fission, budding, fragmentation and spore formation.

Syngamy and conjugation.

Type of cell division 

Mitosis only

Involves Both mitosis and meiosis.

Involvement of sex cells

Involves somatic or peripheral body cells of parents.

Involves germ cells or gametes.

Class of species involved

Occurs in lower invertebrates, chordates, and plants having a simple organizational structure.

Occur in higher plants and all animals.

Fertilization

No fertilization.

Requires fertilization 

Duration/time required

Multiplication is very rapid.

It is usually lengthy depending on the organism.

Degree of variation

Lesser chances for genetic variations

It favours genetic variation 

Offspring

The number of offspring produced may vary from 2 to many.

Comparatively lesser in numbers.

The offspring are genetically similar.

The offspring produced are genetically different from their parents.

 

Types of asexual reproduction in plants

The most common types of natural asexual reproduction in plants include fission, budding, vegetative propagation, spore formation, fragmentation, , multiple fission. Some artificial methods like Cutting, layering, and grafting are also useful in commercial crop production.

1. Binary Fission

Fission requires the organisms to undergo rapid cell division. The 2 types of fission are binary fission and multiple fission. Binary fission begins by forming a ridge or cleft in the middle of the original parent, which subsequently divides into many pieces which are genetically identical. Members of the Kingdom Fungi and simple plants such as algae reproduce by the binary fission as shown below. 

 

https://www.innoclazz.com/assets/course-img/Binary%20fission....jpg

 

2. Multiple fission

In multiple fission, parent cell divides itself to form many smaller units. The process begins with the formation of a cyst in a corner of the parental body. The nucleus present in the centre of the cyst breaks into a number of many smaller nuclei with the help of mitosis. It is seen in protists like sporozoans and algae.

 

https://www.innoclazz.com/assets/course-img/Multiple%20fission.png

 

3. Budding

A bud refers to a small outgrowth at the corner of a parental cell while budding is a process of growth of bud. The tiny bud continues to grow until it attains maturity. Followed by this,  it gets detached gradually from the parent to grow itself into a new organism. Budding is very common in sponges, hydra and yeast. Budding has 2 variants: internal and external. External budding is the usual mechanism which we have already discussed while internal budding forms some gemmules. A gemmule is the small collection of several different types of cells that are enclosed by a protective covering. Internal budding involves a distinctive process called endodyogeny in which daughter cells consume their mother prior to their separation.

 

https://www.innoclazz.com/assets/course-img/Budding.png

 

4. Spore formation

Sporogenesis or spore formation is the process of formation of many tiny spores or projections from the spore case. A spore case is a protective encasement for these spores. When the spores are matured, the spore case of the plant bursts. Offsprings travel by the wind force to reach the soil where they can further reproduce into many new plants. Fungi like Rhizopus and Mucor undergoes spore formation.

 

https://www.innoclazz.com/assets/course-img/spore_formation.jpg

 

5. Regeneration

In regeneration, the body of a parent organism is cut into many small pieces. These tiny pieces regrow into individual organisms with the help of mitosis as seen in hydra and planaria.

 

https://www.innoclazz.com/assets/course-img/Regeneration%20inplanaria.jpg

 

6. Fragmentation

In a fragmentation, the mature parent breaks itself into two or more pieces. It seems almost like regeneration but there is a little difference between the 2. Regeneration involves a process where a part of the parental body is cut to form a new offspring while in the fragmentation, the entire body of the parent is equally shattered into pieces that eventually grow bigger. Spirogyra undergoes fragmentation.

 

https://www.innoclazz.com/assets/course-img/fragmentation...jpg

 

7. Vegetative Propagation

This is commonly seen in some plants such as ginger and potatoes where a new plant is propagated out of a fragment of the parent. The process is facilitated by different parts of the plant body.  In stems, the runners grow horizontally above the ground which results in the formation of buds at the nodes while some new plants emerge out of swollen or modified roots called tubers. Furthermore, leaves of some plants get detached from the parent plant to redevelop into an individual plant. Bulbs in the underground are not only capable of storing food but at their centre, they form an apical bud that produces leaves and flowers. 

 

https://www.innoclazz.com/assets/course-img/Vegetative%20propagation...jpg

Apart from these natural methods, some artificial methods like Cutting, layering, and grafting are also useful for commercial and large scale vegetative production. 

 

Read More

  1. Reproductive Health

  2. Accumulation of Variation during Reproduction 

  3. Sexual reproduction in plants 

  4. Human reproduction  

 

Questions

  1. Sexual reproduction doesn't play any role in variation -explain.

  2. Mention the different types of asexual reproduction techniques.

  3. Distinguish between asexual and sexual reproduction.

  4. Explain the types of fission as asexual reproduction in plants.

  5. Describe budding with an example.

  6. What is the difference between fragmentation and regeneration? 

 

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