Asexual reproduction

Introduction to the reproduction

Reproduction is the most essential process of life, without which organisms cannot exist. Reproduction is defined as the development of offspring out of one or 2 parents. There are 2 principal types of reproduction, sexual reproduction and the asexual reproduction" Sexual reproduction is the result of the fusion between the male and female gametes through the sexual contact. On the other hand, Asexual reproduction does not involve sexual contact between the 2 parents however, ofsprings are formed by a variety of biological divisions. 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 where there is high degree of variation between the 2 generations. This is because, in sexual reproduction, each cell is under the influence of a substantial differentiation. This can result in a completely different type of progeny. Sexual reproduction is very important aspect of evolution as it improves the fitness and the survival skills of the resulting species.  On the contrary, asexually  reproduced breed is less likely to be different from that of parent as there is no participation of 2 highly different parents.

 

 

Types of reproduction

 

 

Asexual reproduction

Asexual reproduction doesn’t involve the sharing of genetic material between the 2 parents, rather, an offspring is formed out of a single organism. The parent is being broken into 2 or more parts in a proportionate manner without the influence of variation. Hence, there is a high chance of exact duplication of an offspring from the parent. Asexual reproduction is not a favourable reproduction from the evolution point of view as they essentially produce the progeny that resembles parent. Asexual reproduction is the most primitive form of reproduction because the majority of the unicellular organisms such as algae, fungi, viruses, and bacteria are reproduced by this method. Many plants and some of the animals undergo asexual reproduction.

 

Advantages of Asexual Reproduction

1. It is quick and rapid mode of reproduction that result in the formation of progeny in huge numbers. There is the minimal chance for the survival of the whole colony as many of the organisms are  vanished to ultimately result in the survival of a decent number of offspring. Microbes like bacteria are reproduced by this type of reproduction.

2. Unlike sexual reproduction, asexual reproduction doesn't necessitate the physical contact between the 2 opposite genders hence it is relatively easy and simple.

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

4. Asexual reproduction can transfer positive genetic influences through generations.​

 

 

Disadvantages of Asexual Reproduction

1. Asexual reproduction results in the lesser proportion of variation between the parents and the offspring. This is because the progeny is just a photocopy of the parent with minimal opportunity for the differentiation at the embryo level. 

2. Asexually reproduced species exhibit poor adaptations skills against the adverse environmental conditions 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.

3. Some unicellular organisms have born with a higher degree of genetic errors while replicating through asexual means. This may be due to the wrongly copied genetic sequences during the reproduction. 

4. It is highly impossible to control the pace of replication during the asexual reproduction, this can result in an uncontrolled, faulty production of progeny even though the parent is healthy

5. Asexually born organisms are less capable  to escape from the unhealthy effects of environment.

 

 

Differences between sexual and asexual reproduction

CRITERIA

ASEXUAL REPRODUCTION

SEXUAL REPRODUCTION

Parent cell involvement

There is no need of fusion between the male and a female parent.

There will be a fusion between the 2 matured germ cells derived from the 2 opposite genders.

Types

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

Syngamy and conjugation.

Number of organisms or parents involved

Involves only one parent (uniparental).

Involves 2 parents with one being the  male and the other one is female (biparental)

Cell division type

Mitosis only

Both mitosis and meiosis.

Involvement of sex cells

Somatic or peripheral body cells of parents.

Germ cells or gametes of parents.

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.

Fertilization takes place.

Time is taken to complete

Multiplication is very rapid.

Multiplication is not rapid

Offspring

The number of offspring may vary from two 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

Some of the types of asexual reproduction are, Fission, Budding, Vegetative propagation, spore formation, Fragmentation, Layering, multiple fission along with artificial methods like grafting. 

 

1. Binary Fission

In binary fission, the organisms undergo a cell division without the involvement of 2 genders. A binary Fission occurs when the parental body is divided into 2 pieces by forming a cleft in the middle of the cell. Fission is possible only if the parent body attains complete maturity.  Members of the Kingdom Fungi and simple plants such as algae reproduce by the binary fission as shown below. 

Binary Fission of amoeba-Souce NCERT

 

2. Multiple fission

Multiple fission is a process of asexual reproduction in which parent cell divides itself to form much smaller units. Multiple fission begins with the formation of a cyst in a corner of the parental body. Inside this cyst, the nucleus breaks into a number of many smaller nuclei alongside the cell division. For example, plasmodium undergoes multiple fission.

Multiple Fission -Image from NCERT

 

3. Budding

A bud refers to a small outgrowth and budding is a process of growth of  bud. The tiny bud keeps growing until it attains a proper growth and maturity. Later on, the bud is slowly detached from the parent to grow itself into a new organism. Budding is very common in hydra and yeast.

Budding of hydra

 

 

4. Spore formation

In this method, the parental plant produces thousands of spores enclosed within the spore case. When the spores are matured, the spore case of the plant bursts. As a result, the spores travel by the wind force reaching soil that can further germinate and produce new plants. Fungi like Rhizopus, Mucor, undergoes spore formation.

  A Rhizopus fungus forming spores

 

 

5. Regeneration

In a regeneration, the body of a parent organism is cut into many small pieces. The cut-pieces will regrow into individual organisms through cellular multiplication and growth. It is seen in hydra and planaria.

Regeneration in Planaria

 

 

6. Fragmentation

In a fragmentation, the organism breaks into two or more pieces as they attain maturation, it is slightly different from the regeneration because, in the case of regeneration a part of the body is cut to form a new offspring,  but in the case of fragmentation, the whole body is equally fragmented into pieces that eventually grow bigger. Spirogyra undergoes fragmentation.

 Spirogyra, undergoing fragmentation

 

 

7. Vegetative Propagation

This is a form of asexual reproduction occurring in plants in which a new plant grows from a fragment of the parent. Later on, each fragment will grow into individual plants. For example, potatoes reproduce by vegetative propagation.

 reproduce 

Potato undergoing vegetative propagation( shutter stock)

In addition to these natural methods, some artificial methods like Cutting, layering, and grafting are also useful but these are for commercial purposes and induced artificially by the plant nurseries. All organisms have to reach a certain stage of growth and maturity in their life before they can reproduce sexually.

 

 

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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