Asexual Reproduction is a type of reproduction that does not involve the fusion of sex cells or gametes (fertilisation) such as in sexual reproduction. One single parent cell or organism gives rise to another by simple mitotic cell division.
The Difference Between Natural and Artificial Cloning
While artificial and natural cloning both lead to the same result, with the formation of a clone, meaning an organism with an identical or almost identical, genome to another organism, the circumstances of this creation differ greatly between the two. The main difference between the two is that natural cloning does not involve human intervention, whereas artificial cloning is a genetic engineering technique.
Artificial and Natural Cloning Definition
Artificial Cloning - Artificial cloning is the production of a clone resulting from genetic engineering techniques. Some examples of this type of cloning are somatic cell nuclear transfer and artificial embryo splitting.
Natural Cloning - Natural cloning is the production of a clone without any human intervention. Scientists take advantage of natural cloning mechanisms in several artificial cloning techniques.
Check out the article for Artificial Cloning to learn more about what kind of techniques we can do to mimic natural cloning. Also, take a look at the Genetic Engineering and Uses of Genetic Engineering articles to see what other research techniques scientists have developed and their usefulness to us!
Examples of Natural Cloning
Natural cloning occurs through many mechanisms within nature, ranging from single-celled organisms to complex, multicellular organisms. Some of these mechanisms are outlined below and then explored in further detail. While this article does split the mechanisms into plants and animals, it is worth remembering that there are overlaps between the two in the methodologies used.
- Binary Fission
- Budding
- Fragmentation
- Parthenogenesis
- Vegetative Propagation
- Spore Production
- Monozygotic Twin Formation
Natural Cloning in Animals
Binary Fission
Binary fission is a form of asexual reproduction in which the parent organism splits itself into two daughter cells. It is the primary reproduction method of prokaryotes such as bacteria and archaea, however, it also occurs in flatworms and protists.
To begin the process, the cell gradually enlarges to have enough membrane to contain the cellular contents necessary for the two daughter cells. The cell then duplicates its genetic material before attaching each copy to opposing ends of the parent cell. Finally, the cell pinches itself off into two new cells by forming a new cell wall across the middle of the parent cell and then pulling the cell apart into the two new daughter cells.
Go take a look at our article on Classification Systems to learn what kind of organisms there are. Do you know what Protists are?
Budding
Budding is a similar form of reproduction to binary fission, with one key difference. Instead of duplicating the DNA and then splitting the parent cell into two identically sized daughter cells, thereby eliminating the parent cell, the new cell grows as a small projection from the parent cell. It is a reproductive method used primarily by members of the animal genus Hydra, along with yeasts (a type of unicellular fungus). The genetic material of the organism is duplicated and then placed into the small outcropping of the cell membrane, which over time matures into a new cell and eventually detaches from the main body, forming a new smaller cell, and leaving the parent cell behind to reproduce again. This process is shown below in figure 1.
Fragmentation
Fragmentation is, as the name suggests, the formation of clonal organisms from smaller fragments of the parent organism. This may occur either intentionally, through the formation of sections of the organism designed to be intentionally shed or broken off, to later develop into new clones or unintentionally as a result of trauma to the organism. These fragments then regrow into two new whole organisms which are genetically identical to the organism the fragments come from, thereby creating clones. Fragmentation occurs in many organisms, including starfish, some worms, sponges and fungi.
Parthenogenesis
Parthenogenesis is a form of reproduction in which a gamete develops into a new organism without undergoing fertilisation. This usually occurs with female gametes, however, does also occur with male gametes. There are many subtypes of parthenogenesis, not all of which result in clonal organisms. Parthenogenesis occurs in plants, insects and many types of animals. Organisms that use this form of reproduction may do so in an obligate manner (because they don't have any other way), or a facultative manner, where the reproductive method used changes depending on environmental conditions.
Monozygotic Twin Formation
Twins can occur in several ways; however, only monozygotic twins are genetically identical and therefore technically clones. Monozygotic twins occur when an egg cell is fertilised during sexual reproduction, but instead of forming a single offspring as normal it splits into multiple offspring at the blastocyst stage, hence the term monozygotic, meaning multiple offspring from one zygote. This is not limited to twins and can result in more than two identical offspring; however, this is a rare occurrence on top of the splitting of a zygote, which already only occurs in around 3 in 1000 births.
The twinning process, meaning the formation of twins is not fully understood even today. There are even theories that suggest that fraternal or dizygotic twinning can be formed from two sperm cells fusing with one egg cell creating a chimeric morula!
Natural Cloning in Plants
Vegetative Propagation
Many plants can regrow whole new organisms from small sections of plant tissue in a process known as vegetative propagation. Plants contain tissue known as meristems, which contain a number of totipotent cells.
Totipotent cells possess the ability to differentiate into any form of cell within an organism. Therefore, small pieces of this tissue contained in plant fragments can eventually grow into whole new organisms.
Plant species that possess larger amounts of meristematic tissue have an easier time reproducing through vegetative propagation. Plants may produce structures intentionally designed to take advantage of vegetative propagation, such as plantlets or runners (Figure 2), but clones can also arise through other parts of the plant that are removed, an ability that is also utilised to artificially clone plants!
Meristems are a type of stem cell! Learn more about them by checking out our article on Stem Cells!
Sporulation
Spores are small, unicellular reproductive cells that may be used during asexual and sexual reproduction. They are generally more robust than the parent cell, allowing the population to survive environmental stresses that otherwise may not be survivable. They are not gametes because spores do not require fusion with another cell to create a new organism as spores formed during sexual reproduction are already fertilised by gamete fusion before formation.
Spores used in asexual reproduction are formed through mitosis, and when exposed to suitable environmental conditions develop into new organisms identical to the parent. This strategy is used in bacteria, plants, fungi, protozoa and algae.
As a final review, take a look at the Reproduction article to deepen your understanding of sexual vs asexual reproduction!
Natural Cloning - Key takeaways
- Clones are genetically identical organisms. Cloning may be natural or artificial.
- Natural cloning is usually part of asexual reproduction. Natural cloning may also be due to the random splitting of the zygote, forming identical twins.
- Natural cloning happens during binary fission, budding, fragmentation, parthenogenesis, vegetative propagation, and sporulation.
References
- Figure 1: Saccharomyces cerevisiae budding (https://commons.wikimedia.org/wiki/File:S_cerevisiae_under_DIC_microscopy.jpg) by Masur (https://commons.wikimedia.org/wiki/User:Masur). Public Domain.
- Figure 3: Fern Spores (https://commons.wikimedia.org/wiki/File:Fern_sporangia_in_Saratoga_CA.jpg) by Catleeball (https://commons.wikimedia.org/wiki/User:Catleeball). Licensed by CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0/deed.en).
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Frequently Asked Questions about Natural Cloning
What is natural cloning?
Natural cloning is the creation of clonal offspring without artificial human intervention.
Do clones occur naturally?
Clones do occur naturally, via many mechanisms, including the occurrence of monozygotic twins, binary fusion, fragmentation among others.
How does cloning differ from natural reproduction?
Cloning results in a clone of an organism, whereas natural reproduction may produce a clone, but may also produce non-clonal offspring. This makes natural cloning a sub-type of natural reproduction.
What are natural clones?
Natural clones are clones formed without artificial intervention. A clone is an organism that is genetically identical to its parent organism.
What are the 3 types of cloning?
Three main types of cloning are genetic cloning, which clones genetic material, reproductive cloning, which clones whole organisms and therapeutic cloning for the production of stem cells.
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