Asexual Reproduction (Meaning and Explanation)

We explain what asexual reproduction is, the types that exist, its advantages and disadvantages. Also, what is cloning.

apomixis asexual reproduction of dandelion — Some plants such as dandelions reproduce asexually through their seeds.

What is asexual reproduction?

Asexual reproduction is one that requires a single organism, which does not need to mate to form new individuals. Since there is no intervention of sex cells, in sexual reproduction there is no exchange or combination of genetic information.

When an organism reproduces asexually, it does so through methods that consist of the replication or duplication of its genetic content to give rise to new individuals genetically identical to itself.

Reproduction consists of the production of new individuals of the same species than the progenitor, which allows the species to multiply and perpetuate. Reproduction constitutes one of the main stages in the life cycle of every living being and, although it is not essential for an individual to survive, it is essential for a species to remain on Earth.

Organisms can reproduce in various ways, which can be grouped into two types of reproduction: sexual or asexual, depending on the number of individuals involved and whether the offspring are genetically identical to the parent organism or organisms.

Sexual reproduction, like that of human beings, involves sexual contact between two individuals, a female and a male, each of which contributes a gamete or sexual cell. The union between the female and male gametes (egg and sperm respectively) gives rise to the embryo, which when developed will form a new individual of the same species, whose genetic material will result from the combination of that of its parents. Thus, in sexual reproduction each parent provides half of the genetic information, and offspring are formed that are genetically different from their parents.

asexual reproduction It is typical of unicellular organisms, such as prokaryotes and protists and is common in fungi, invertebrates and plants. Although in more complex forms of life, sexual reproduction is usually more frequent, there are also some specific cases of animals that reproduce asexually.

Types of asexual reproduction

asexual reproduction plant fragmentation — Many plants can create a new individual from a fragment.

Asexual reproduction can occur through different mechanisms, among which are the following:

Gemmation It consists of the production of protuberances or bud formations on the body of the parent itself, from which an independent individual then emerges, capable of detaching and living autonomously, or of remaining attached and starting a colony. Budding is a common process in poriferans, cnidarians and bryozoans. In addition, some single-celled organisms, such as yeast and some bacteria, reproduce by this method.
Fragmentation It consists of the production of new individuals from fragments of the parent's body, thus reconstructing the entire body from a significant piece of it. These fragmentations can be intentional or accidental. Fragmentation is a mechanism of asexual reproduction present in many invertebrates, such as starfish, ophiuras and planarians. In addition to animals, there are plants that can reproduce by the fragmentation mechanism, directed by human intervention, and which is better known as “artificial vegetative multiplication.”
It is important not to confuse the processes of regeneration through fragmentation with those of asexual reproduction. For example, some lizards are capable of regenerating their tail if they accidentally lose it, but this phenomenon does not imply reproduction since it does not lead to the appearance of new individuals.
Binary fission It is the simplest asexual reproduction mechanism and consists of the duplication of the genetic material (DNA molecules) of the parent, followed by the division of its organelles and finally the splitting of the cytoplasm, thus obtaining two identical cells where there was previously only one. Binary fission is carried out by prokaryotic organisms, which include bacteria and archaea. There are also some unicellular eukaryotic organisms that reproduce by a similar mechanism: one cell gives rise to two identical daughter cells of similar sizes. However, in these organisms the presence of a true cell nucleus makes the process a little more complex and elaborate.
Sporulation It consists of reproduction through resistant, unicellular structures, capable of resisting extreme conditions, called spores or endospores. Sporulation can be part of the organism's normal life cycle or, in some cases, favored or triggered by unfavorable environmental circumstances. The sporulation mechanism is a form of cell division common in fungi, plants and certain types of bacteria.
Apomixis This mechanism is exclusive to plants and consists of a form of asexual reproduction through seeds, which does not involve fertilization or meiosis. In plants that reproduce by this method, the individual produces seeds that are genetically identical to itself, which allow the species to extend, but have little adaptability to the environment. There are different types of apomixis in the plant kingdom and it is a type of asexual reproduction that is quite common in this group of living beings.
Parthenogenesis This mode of asexual reproduction involves the development of unfertilized female sex cells, that is, possessing the same genetic material as their parent, through segmentation of the unfertilized egg. This mechanism of asexual reproduction is present in both invertebrate and vertebrate groups: it is a common procedure in certain fish, reptiles, insects, crustaceans and amphibians, especially in times of risk for the species.
Polyembryony It consists of a mode of reproduction in which two or more embryos develop from a single zygote. In reality, it can be said that it constitutes a combination of sexual and asexual reproduction: the first is necessary for fertilization and formation of the zygote, and the second takes place when the embryo divides into several genetically identical ones, and gives rise to two or more individuals. genetically identical to each other, but different from their parents. Depending on the number of embryos generated, polyembryony can be simple or multiple. This mode of reproduction is common in certain insects, plants and curiously in armadillos, whose litter is always monozygotic (comes from the same embryo). It can also occur in humans, as happens in univiteline or identical twins, which come from the same zygote (and should not be confused with dizygotic twins).

Advantages of asexual reproduction

asexual reproduction binary fission advantages — Asexual reproduction like binary fission requires very few resources.

asexual reproduction It is fast and simple, since it does not require the production of specialized cells (gametes), nor does it require spending energy to achieve fertilization, nor other similar efforts. Thus, this type of reproduction allows an isolated individual to perfectly give rise to new descendants, sometimes many of them, although always genetically identical to itself and to each other.

This results particularly useful in situations of biological risk or need for rapid expansion for example, during the colonization of a territory or the massification of specimens in the face of imminent danger.

Disadvantages of asexual reproduction

The great disadvantage of asexual reproduction is its absence of genetic variability that is, the fact that the descendants are identical to the parent, except in the case of unforeseen mutations.

Thus, the species evolves at a much slower rate and much less effective since natural selection cannot favor those fittest individuals. This could wipe out a colony or even a species very quickly, given that its lower genetic variability can prevent rapid adaptation to a changing environment.

Clones and cloning

In genetics, a clone is defined as a set of genetically identical individuals, coming from another individual through asexual reproduction mechanisms. Although these processes are very frequent in nature (in fact, asexual reproduction is much earlier than sexual reproduction), the term clone was created in 1903 by HJ Weber, with the intention of contributing to the development of the lexicon of genetics, a science that was beginning to develop at that time. Currently, asexual reproduction can be called clonal reproduction, although it is not widely used.

You may be interested: Central Nervous System

Cloning, which derives from the term clone, is the action of producing a biological entity that is genetically identical to another, from an existing one. Although this process can be carried out without greater technical knowledge (for example, when vegetative multiplication of plants is carried out), when talking about cloning, more is usually done in reference to artificial techniques used in a laboratory to produce genetically identical individuals.

In the case of vertebrates, artificial cloning is based on removing the nucleus of an egg and replacing it with that of an adult cell belonging to the individual to be cloned. This modified egg (now equivalent to a viable zygote) is then transferred to the body of a female where it will continue its development until birth. This technique began to be applied in frogs in 1952, but was only successful in mammals in 1996 with the famous Dolly sheep.

From a practical point of view, cloning in humans should not have insurmountable technical obstacles in the long term. However, the possibility of using the technique in our species, which is called “reproductive cloning,” has given rise to an intense ethical, religious, social and political debate in which multiple actors participate and which is still far from being resolved.