Artificial cloning occurs when the creation of the clone is due to human intervention, rather than via natural occurrence. Artificial cloning is carried out for many purposes, using a variety of techniques. It also may be carried out on several individual structural levels, including genes, individual cells, tissues and whole organisms! Keep reading to learn more about the Types of artificial Cloning, artificial cloning in animals, and more.
Artificial Cloning: Definition
To clone an organism is to create an organism which is genetically identical to another organism, a copy! Artificial Cloning is a type of cloning which occurs due to human interference, rather than through naturally occurring processes. It generally takes advantage of processes which occur during natural cloning.
A clone is the product of a cloning process! For example, bacteria create clones of themselves all the time when reproducing and dividing. This is known as asexual reproduction and is an example of natural cloning.
Artificial Cloning Types and Processes
There are many types of artificial cloning, which clone things ranging from individual genetic material (DNA) to whole organisms, each of which is explored below.
Gene Cloning
Gene cloning, more correctly termed molecular cloning, involves the replication of genetic material. This is often done to entire genes for a variety of purposes such as genetic engineering, however, it may be applied to any section of DNA or other types of genetic material.
Molecular Cloning is a major research technique in biomedical science. Check out our article Genetic Engineering to learn more!
When applied to DNA, this form of cloning is usually carried out by either PCR or by inserting the DNA into a host organism such as bacteria or yeast which then copies the DNA for later extraction.
RNA is usually cloned via reverse transcription PCR, in which the RNA is first converted back into DNA, and then amplified in the same manner as for regular PCR. This DNA can then be converted back into RNA if needed.
Regardless of the process used, these processes all result in many identical copies of the original genetic material.
Single Cell Cloning
Single-cell cloning may be applied to either unicellular organisms, in which case you are effectively cloning the entire organism, or to cells taken from a larger (multicellular) organism.
Cloning Unicellular Organisms
Cloning unicellular organisms such as yeast and bacteria is not really artificial cloning, more providing ideal conditions for the natural asexual reproduction they already perform.
The only alteration to the naturally occurring process in the intentional cloning of yeasts and bacteria is using a method such as streak plating to ensure that all cells in a given colony are clones of a single initial cell.
Cloning Cells From Multi-Cellular Organisms
Cloning cells from multi-cellular organisms may be known as cell culture when applied to cells taken from eukaryotes, plant tissue culture when growing plant cells and fungal culture when growing fungal cells. The exact process used varies depending on the source of the cells being cloned, however, the same basic principles are utilised.
The cells are isolated from the multi-cellular organism and then placed into a vessel containing media that provides all the nutrients needed for them to multiply along with aiding to maintain the environment they require.
This vessel is then placed into an incubator to also maintain the ideal environment. The cells may either float freely within the media or attach to surfaces within the vessel.
These cells are generally immortalised, meaning they have unlimited divisions in vitro without entering senescence (stopping cell division). These cell types are known as cell lines. Cells used in cultures that are non-immortalised are termed cell strains. Immortal cell lines, while they will not become senescent due to the number of divisions undertaken, may still enter senescence due to cell density. This is avoided through a process known as passaging, in which a small number of cells are removed from culture and placed into a new vessel, thereby massively lowering the cell density.
Figure 1: HeLa cells stained using Hoescht fluorescent stain.
Animal cells used in culture are usually sourced from cancerous organisms as this is the easiest way for immortalisation to occur, however, an immortalising gene may also be introduced to cells.
Examples of cell lines shown are HeLa cells, sourced from Henrietta Lacks' cervical cancer and Cho cells, sourced from Chinese hamster ovary cells.
Figure 2: Cho cells adhered to a surface, viewed using phase-contrast microscopy.
Plant tissue culture, also known as micropropagation, places plant tissue samples onto media that contain plant growth hormones and all required nutrients. These plant tissue sections, known as explants, eventually develop into masses of tissue known as plantlets. These plantlets can then be transferred into the soil, where they grow into identical copies of the parent plant or are maintained as a stock of plant cells for use in other experiments. These same principles may also be used to grow tissues within the lab, removing the need for an entire organism to be bred or cloned to source them.
Learn more about plant growth hormones by checking out our article on Plant Hormones!
Whole Organism Artificial Cloning
Instead of cloning single cells, sometimes entire organisms are cloned. Whole organism cloning may be performed for the purpose of either reproductive cloning or therapeutic cloning. Whole organism cloning may be theoretically applied to any living organism, including humans, however, this is illegal and highly controversial.
Reproductive Cloning
Reproductive cloning is cloning for the purpose of creating more copies of a whole organism, generally for either research or to create more copies of an organism with desirable characteristics.
In livestock farming, this is used to create copies of breeding stock, which are then conventionally bred producing offspring that can enter the food supply. This allows for desirable genetics to be passed on more rapidly and in larger volumes than breeding single instances of the animal.
Cloning is used in many plants to create large volumes of plants with desirable characteristics, for either food or ornamental purposes.
Therapeutic Cloning
Therapeutic cloning is cloning for the purpose of extracting stem cells from the formed embryo. These stem cells can then be used for a wide array of uses including tissue engineering, cell replacement therapies, toxicology studies and many others.
Once the cloned embryo is created, it is cultured for around five days to form a blastocyst. The pluripotent stem cells are then extracted from the inner mass after removing the outer layer through either immunosurgery or manual dissection of the cell bundle. These pluripotent cells are then cultured, ready to be stimulated to differentiate into virtually any needed cell type.
Stem cells are a powerful type of cell. Learn more about them by checking out our article Stem Cells!
Whole Organism Cloning Methods
Whole organisms can be cloned using any one of several methods, all of which have distinct benefits and drawbacks.
Somatic Cell Nuclear Transfer
In somatic cell nuclear transfer, an ovum, or egg cell has its nucleus removed. The nucleus from a somatic (non-gamete) cell is removed and inserted into the egg cell. Since the egg now has the full number of genes required to develop, it begins to form a new organism. The egg is then implanted into a surrogate and brought to term. The resultant animal is a clone of the source of the somatic cell nucleus.
Embryo Splitting
Embryo splitting creates clones in the same manner as monozygotic twins are produced. The difference is instead of the division of the blastocyst occurring naturally, the blastocyst is split into two using microsurgery to artificially create a pair of twins.
Plant Cloning
Plants can be cloned by taking small cuttings of plant tissue and placing these in media which triggers the growth of a new plant from the cutting. This plant is a clone of the parent plant, and the cutting may range in size from a branch all the way down to a few cells.
Artificial Cloning in Animals
A variant of somatic cell nuclear transfer, known as the Roslin technique, was used to create Dolly the sheep, the first mammal cloned from an adult somatic cell. The Roslin Institute removed the ovum nucleus, but instead of extracting the somatic nucleus, they placed it into a dormant state by limiting nutrient access. The cells were then shocked, triggering fusion of the cells, resulting in a ready-to-develop egg. This egg was then placed into a surrogate and brought to term resulting in Dolly the sheep.
Figure 3: The taxidermied body of Dolly the sheep.
Example of Artificial Cloning
Another form of cloning often used is PCR (Polymerase Chain Reaction). PCR is used routinely in laboratories for a variety of purposes.
An example you may be familiar with from recent events is COVID-19 testing. As COVID-19 is an RNA virus, a specialised form of PCR known as RT-qPCR is used. This uses reverse transcriptase to create DNA from RNA, which is then amplified by DNA polymerase.
The q in RT-qPCR stands for quantitative, meaning that the amount of DNA produced is measured throughout the process, often by incorporating fluorescent molecules into the copied DNA.
When a certain threshold measurement is reached, the sample is considered positive for COVID-19 RNA and therefore the person is considered positive for COVID-19.
Uses Of Artificial Cloning
Clones have many uses in many sectors of society. Natural cloning can be manipulated in ways useful to humanity, and artificial cloning techniques provide many uses both in and out of research and academia. Some of these uses are summarised below.
- Cloning organisms with desired genes allow these traits to be preserved, or the number of organisms with the trait to be increased, without the traits being modified during breeding.
- Clones may be used to produce medical treatments including monoclonal antibodies and new organs or tissues.
- Cloning may potentially be used to resurrect extinct species, although perhaps not to the degree shown in Jurassic Park!
- Cloning may allow organisms which cannot breed traditionally to create offspring.
The Downsides And Ethical Issues Of Cloning
While cloning technology allows for great strides to be made in healthcare, industry, research, conservation and many other areas, it is also a source of great ethical concern and may have many downsides. For example, Is it ethical to create life purely to use it for the harvest of its organs or tissues? Some of these questions are summarised below.
- Cloning extinct animals does not solve a lack of genetic diversity, and cloning of non-extinct animals limits a population's genetic diversity.
- Clones are genetically the same age as the organism the genes were taken from, meaning genetic disorders or mutations that have occurred during the source's lifetime are passed on.
- The rights and legal status of cloned people would be open to question.
- Cloned organisms may face issues later on in life that are not immediately obvious.
- Cloning has a very low success rate and so large numbers of unsuccessful clones will be created and must be disposed of, which also poses ethical issues.
- Cloning limits individual identity.
Artificial Cloning - Key takeaways
- Artificial cloning is the production of clones via human intervention, rather than naturally.
- Artificial cloning may be used to create clones on many organisational levels, from genes to a whole organism.
- One of the most widely used examples of cloning is PCR, and the first example of a clone being produced from an adult somatic cell is Dolly the sheep.
- Cloning can be hugely useful in many areas such as industry, medicine and agriculture, however, it raises a number of ethical and legal dilemmas.
- Artificial cloning often takes advantage of methods which produce natural clones.
References
- Figure 1: HeLa Cells (https://commons.wikimedia.org/wiki/File:HeLa_cells_stained_with_Hoechst_33258.jpg) by TenOfAllTrades (https://en.wikipedia.org/wiki/User:TenOfAllTrades). Public Domain.
- Figure 2: Cho Cells (https://commons.wikimedia.org/wiki/File:Cho_cells_adherend1.jpg) by Alcibiades (https://commons.wikimedia.org/wiki/User:Alcibiades). Public Domain.
- Figure 3: Dolly the Sheep (https://commons.wikimedia.org/wiki/File:Dolly_face_closeup.jpg) by Toni Barros (https://www.flickr.com/people/12793495@N05). Licensed by CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0/deed.en).
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