Cloning: Difference between revisions

In biology, cloning is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments (molecular cloning), cells (cell cloning), or organisms. The term also refers to the production of multiple copies of a product such as digital media or software.

The term clone, invented by J. B. S. Haldane, is derived from the Ancient Greek word κλών klōn, "twig", referring to the process whereby a new plant can be created from a twig. In horticulture, the spelling clon was used until the twentieth century; the final e came into use to indicate the vowel is a "long o" instead of a "short o".^[1][2] Since the term entered the popular lexicon in a more general context, the spelling clone has been used exclusively.

In botany, the term lusus was traditionally used.^{[3]: 21, 43}

Natural cloning

Cloning is a natural form of reproduction that has allowed life forms to spread for more than 50 thousand years. It is the reproduction method used by

Molecular cloning refers to the process of making multiple molecules. Cloning is commonly used to amplify

Cloning of any DNA fragment essentially involves four steps[8]

1. fragmentation - breaking apart a strand of DNA
2. ligation - gluing together pieces of DNA in a desired sequence
3. transfection – inserting the newly formed pieces of DNA into cells
4. screening/selection – selecting out the cells that were successfully transfected with the new DNA

Although these steps are invariable among cloning procedures a number of alternative routes can be selected; these are summarized as a cloning strategy.

Initially, the DNA of interest needs to be isolated to provide a DNA segment of suitable size. Subsequently, a ligation procedure is used where the amplified fragment is inserted into a

Cloning a cell means to derive a population of cells from a single cell. In the case of unicellular organisms such as bacteria and yeast, this process is remarkably simple and essentially only requires the inoculation of the appropriate medium. However, in the case of cell cultures from multi-cellular organisms, cell cloning is an arduous task as these cells will not readily grow in standard media.

A useful tissue culture technique used to clone distinct lineages of cell lines involves the use of cloning rings (cylinders).

Therapeutic cloning is achieved by creating embryonic stem cells in the hopes of treating diseases such as diabetes and Alzheimer's. The process begins by removing the nucleus (containing the DNA) from an egg cell and inserting a nucleus from the adult cell to be cloned.[11] In the case of someone with Alzheimer's disease, the nucleus from a skin cell of that patient is placed into an empty egg. The reprogrammed cell begins to develop into an embryo because the egg reacts with the transferred nucleus. The embryo will become genetically identical to the patient.^[11] The embryo will then form a blastocyst which has the potential to form/become any cell in the body.^[12]

The reason why SCNT is used for cloning is because somatic cells can be easily acquired and cultured in the lab. This process can either add or delete specific genomes of farm animals. A key point to remember is that cloning is achieved when the oocyte maintains its normal functions and instead of using sperm and egg genomes to replicate, the oocyte is inserted into the donor’s somatic cell nucleus.^[13] The oocyte will react on the somatic cell nucleus, the same way it would on sperm cells.^[13]

The process of cloning a particular farm animal using SCNT is relatively the same for all animals. The first step is to collect the somatic cells from the animal that will be cloned. The somatic cells could be used immediately or stored in the laboratory for later use.^[13] The hardest part of SCNT is removing maternal DNA from an oocyte at metaphase II. Once this has been done, the somatic nucleus can be inserted into an egg cytoplasm.^[13] This creates a one-cell embryo. The grouped somatic cell and egg cytoplasm are then introduced to an electrical current.^[13] This energy will hopefully allow the cloned embryo to begin development. The successfully developed embryos are then placed in surrogate recipients, such as a cow or sheep in the case of farm animals.^[13]

SCNT is seen as a good method for producing agriculture animals for food consumption. It successfully cloned sheep, cattle, goats, and pigs. Another benefit is SCNT is seen as a solution to clone endangered species that are on the verge of going extinct.^[13] However, stresses placed on both the egg cell and the introduced nucleus can be enormous, which led to a high loss in resulting cells in early research. For example, the cloned sheep Dolly was born after 277 eggs were used for SCNT, which created 29 viable embryos. Only three of these embryos survived until birth, and only one survived to adulthood.^[14] As the procedure could not be automated, and had to be performed manually under a microscope, SCNT was very resource intensive. The biochemistry involved in reprogramming the differentiated somatic cell nucleus and activating the recipient egg was also far from being well understood. However, by 2014 researchers were reporting cloning success rates of seven to eight out of ten^[15] and in 2016, a Korean Company Sooam Biotech was reported to be producing 500 cloned embryos per day.^[16]

In SCNT, not all of the donor cell's genetic information is transferred, as the donor cell's

Organism cloning (also called reproductive cloning) refers to the procedure of creating a new multicellular organism, genetically identical to another. In essence this form of cloning is an asexual method of reproduction, where fertilization or inter-gamete contact does not take place. Asexual reproduction is a naturally occurring phenomenon in many species, including most plants (see vegetative reproduction) and some insects. Scientists have made some major achievements with cloning, including the asexual reproduction of sheep and cows. There is a lot of ethical debate over whether or not cloning should be used. However, cloning, or asexual propagation,^[17] has been common practice in the horticultural world for hundreds of years.

Horticultural

The term clone is used in horticulture to refer to descendants of a single plant which were produced by vegetative reproduction or apomixis. Many horticultural plant cultivars are clones, having been derived from a single individual, multiplied by some process other than sexual reproduction.^[18] As an example, some European cultivars of grapes represent clones that have been propagated for over two millennia. Other examples are potato and banana.^[19] Grafting can be regarded as cloning, since all the shoots and branches coming from the graft are genetically a clone of a single individual, but this particular kind of cloning has not come under ethical scrutiny and is generally treated as an entirely different kind of operation.

Many

Reproductive cloning generally uses "somatic cell nuclear transfer" (SCNT) to create animals that are genetically identical. This process entails the transfer of a nucleus from a donor adult cell (somatic cell) to an egg from which the nucleus has been removed, or to a cell from a blastocyst from which the nucleus has been removed.^[23] If the egg begins to divide normally it is transferred into the uterus of the surrogate mother. Such clones are not strictly identical since the somatic cells may contain mutations in their nuclear DNA. Additionally, the mitochondria in the cytoplasm also contains DNA and during SCNT this mitochondrial DNA is wholly from the cytoplasmic donor's egg, thus the mitochondrial genome is not the same as that of the nucleus donor cell from which it was produced. This may have important implications for cross-species nuclear transfer in which nuclear-mitochondrial incompatibilities may lead to death.

Artificial embryo splitting or embryo twinning, a technique that creates monozygotic twins from a single embryo, is not considered in the same fashion as other methods of cloning. During that procedure, a donor

Dolly the sheep

Dolly was publicly significant because the effort showed that genetic material from a specific adult cell, programmed to express only a distinct subset of its genes, can be reprogrammed to grow an entirely new organism. Before this demonstration, it had been shown by John Gurdon that nuclei from differentiated cells could give rise to an entire organism after transplantation into an enucleated egg.[30] However, this concept was not yet demonstrated in a mammalian system.

The first mammalian cloning (resulting in Dolly the sheep) had a success rate of 29 embryos per 277 fertilized eggs, which produced three lambs at birth, one of which lived. In a bovine experiment involving 70 cloned calves, one-third of the calves died young. The first successfully cloned horse, Prometea, took 814 attempts. Notably, although the first^{[clarification needed]} clones were frogs, no adult cloned frog has yet been produced from a somatic adult nucleus donor cell.

There were early claims that

Dolly was named after performer Dolly Parton because the cells cloned to make her were from a mammary gland cell, and Parton is known for her ample cleavage.^[32]

Species cloned

The modern cloning techniques involving nuclear transfer have been successfully performed on several species. Notable experiments include:

• Tadpole: (1952) Robert Briggs and Thomas J. King had successfully cloned northern leopard frogs: thirty-five complete embryos and twenty-seven tadpoles from one-hundred and four successful nuclear transfers.^[33][34]
• embryologist Tong Dizhou produced the world's first cloned fish by inserting the DNA from a cell of a male carp into an egg from a female carp. He published the findings in a Chinese science journal.^[35]
• Mice: (1986) A mouse was successfully cloned from an early embryonic cell. Soviet scientists Chaylakhyan, Veprencev, Sviridova, and Nikitin had the mouse "Masha" cloned. Research was published in the magazine "Biofizika" volume ХХХII, issue 5 of 1987.^{[clarification needed][36][37]}
• Dolly the sheep from a somatic cell in 1996.^[39]
• Rhesus monkey: Tetra (January 2000) from embryo splitting^{[40][clarification needed][41]}
• BGI in China was producing 500 cloned pigs a year to test new medicines.^[43]
• Gaur: (2001) was the first endangered species cloned.^[44]
• Cattle: Alpha and Beta (males, 2001) and (2005) Brazil^[45]
• Cat: CopyCat "CC" (female, late 2001), Little Nicky, 2004, was the first cat cloned for commercial reasons^[46]
• Ralph, the first cloned rat (2003)^[47]
• Mule: Idaho Gem, a john mule born 4 May 2003, was the first horse-family clone.^[48]
• Horse: Prometea, a Haflinger female born 28 May 2003, was the first horse clone.^[49]
• Afghan hound was the first cloned dog (2005).^[50]
• Wolf: Snuwolf and Snuwolffy, the first two cloned female wolves (2005).^[51]
• Samrupa was the first cloned water buffalo. It was born on 6 February 2009, at India's Karnal National Diary Research Institute but died five days later due to lung infection.^[52]
• Pyrenean ibex (2009) was the first extinct animal to be cloned back to life; the clone lived for seven minutes before dying of lung defects.^[53][54]
• Injaz, is the first cloned camel.^[55]
• Pashmina goat: (2012) Noori, is the first cloned pashmina goat. Scientists at the faculty of veterinary sciences and animal husbandry of Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir successfully cloned the first Pashmina goat (Noori) using the advanced reproductive techniques under the leadership of Riaz Ahmad Shah.^[56]
• Gastric brooding frog: (2013) The gastric brooding frog, Rheobatrachus silus, thought to have been extinct since 1983 was cloned in Australia, although the embryos died after a few days.^[57]

Human cloning is the creation of a genetically identical copy of a human. The term is generally used to refer to artificial human cloning, which is the reproduction of human cells and tissues. It does not refer to the natural conception and delivery of

There are a variety of

Advocates support development of therapeutic cloning in order to generate tissues and whole organs to treat patients who otherwise cannot obtain transplants,

Opponents of cloning have concerns that technology is not yet developed enough to be safe[62] and that it could be prone to abuse (leading to the generation of humans from whom organs and tissues would be harvested),^[63][64] as well as concerns about how cloned individuals could integrate with families and with society at large.^[65][66]

Religious groups are divided, with some opposing the technology as usurping "God's place" and, to the extent embryos are used, destroying a human life; others support therapeutic cloning's potential life-saving benefits.^[67][68]

Cloning of animals is opposed by animal-groups due to the number of cloned animals that suffer from malformations before they die,^[69][70] and while food from cloned animals has been approved by the US FDA,^[71][72] its use is opposed by groups concerned about food safety.^[73][74][75]

Cloning extinct and endangered species

Cloning, or more precisely, the reconstruction of functional DNA from

In 2001, a cow named Bessie gave birth to a cloned Asian gaur, an endangered species, but the calf died after two days. In 2003, a banteng was successfully cloned, followed by three African wildcats from a thawed frozen embryo. These successes provided hope that similar techniques (using surrogate mothers of another species) might be used to clone extinct species. Anticipating this possibility, tissue samples from the last bucardo (Pyrenean ibex) were frozen in liquid nitrogen immediately after it died in 2000. Researchers are also considering cloning endangered species such as the giant panda and cheetah.

In 2002, geneticists at the

In January 2009, for the first time, an extinct animal, the Pyrenean ibex mentioned above was cloned, at the Centre of Food Technology and Research of Aragon, using the preserved frozen cell nucleus of the skin samples from 2001 and domestic goat egg-cells. The ibex died shortly after birth due to physical defects in its lungs.^[85]

One of the most anticipated targets for cloning was once the woolly mammoth, but attempts to extract DNA from frozen mammoths have been unsuccessful, though a joint Russo-Japanese team is currently working toward this goal. In January 2011, it was reported by Yomiuri Shimbun that a team of scientists headed by Akira Iritani of Kyoto University had built upon research by Dr. Wakayama, saying that they will extract DNA from a mammoth carcass that had been preserved in a Russian laboratory and insert it into the egg cells of an African elephant in hopes of producing a mammoth embryo. The researchers said they hoped to produce a baby mammoth within six years.^[86][87] It was noted, however that the result, if possible, would be an elephant-mammoth hybrid rather than a true mammoth.^[88] Another problem is the survival of the reconstructed mammoth: ruminants rely on a symbiosis with specific microbiota in their stomachs for digestion.^[88]

Scientists at the University of Newcastle and University of New South Wales announced in March 2013 that the very recently extinct gastric-brooding frog would be the subject of a cloning attempt to resurrect the species.^[89]

Many such "de-extinction" projects are described in the Long Now Foundation's Revive and Restore Project.^[90]

Lifespan

After an eight-year project involving the use of a pioneering cloning technique, Japanese researchers created 25 generations of healthy cloned mice with normal lifespans, demonstrating that clones are not intrinsically shorter-lived than naturally born animals.^[31][91] Other sources have noted that the offspring of clones tend to be healthier than the original clones and indistinguishable from animals produced naturally.^[92]

In a detailed study released in 2016 and less detailed studies by others suggest that once cloned animals get past the first month or two of life they are generally healthy. However, early pregnancy loss and neonatal losses are still greater with cloning than natural conception or assisted reproduction (IVF). Current research endeavors are attempting to overcome this problem.^[32]

In popular culture

Discussion of cloning in the popular media often presents the subject negatively. In an article in the 8 November 1993 article of

Cloning is a recurring theme in a number of contemporary science fiction films, ranging from action films such as Jurassic Park (1993), Alien Resurrection (1997), The 6th Day (2000), Resident Evil (2002), Star Wars: Episode II (2002) and The Island (2005), to comedies such as Woody Allen's 1973 film Sleeper.^[98]

The process of cloning is represented in different ways in fiction. Many works depict the artificial creation of humans by a method of growing cells from a tissue or DNA sample; the process may instantaneous, or take place through a slow process of growing human embryos in

Cloning humans from body parts is also a common theme in science fiction. Cloning features strongly among the science fiction conventions parodied in Woody Allen's Sleeper, the plot of which centres around an attempt to clone an assassinated dictator from his disembodied nose.[101] In the 2008 Doctor Who story "Journey's End", a duplicate version of the Tenth Doctor spontaneously grows from his severed hand, which had been cut off in a sword fight during an earlier episode.^[102]

Cloning and identity

Science fiction has used cloning, most commonly and specifically human cloning, due to the fact that it brings up controversial questions of identity.

In 2012, a Japanese television series named "Bunshin" was created. The story's main character, Mariko, is a woman studying child welfare in Hokkaido. She grew up always doubtful about the love from her mother, who looked nothing like her and who died nine years before. One day, she finds some of her mother's belongings at a relative's house, and heads to Tokyo to seek out the truth behind her birth. She later discovered that she was a clone.[106]

In the 2013 television series Orphan Black, cloning is used as a scientific study on the behavioral adaptation of the clones.^[107] In a similar vein, the book The Double by Nobel Prize winner José Saramago explores the emotional experience of a man who discovers that he is a clone.^[108]

Cloning as resurrection

Cloning has been used in fiction as a way of recreating historical figures. In the 1976 Ira Levin novel The Boys from Brazil and its 1978 film adaptation, Josef Mengele uses cloning to create copies of Adolf Hitler.^[109]

In

The use of cloning for military purposes has also been explored in several works. In Doctor Who, an alien race of armour-clad, warlike beings called Sontarans was introduced in the 1973 serial "The Time Warrior". Sontarans are depicted as squat, bald creatures who have been genetically engineered for combat. Their weak spot is a "probic vent", a small socket at the back of their neck which is associated with the cloning process.^[111] The concept of cloned soldiers being bred for combat was revisited in "The Doctor's Daughter" (2008), when the Doctor's DNA is used to create a female warrior called Jenny.^[112]

The 1977 film

External links

Wikimedia Commons has media related to Cloning.

Library resources about
Cloning

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• Resources in your library
• Resources in other libraries

• "Cloning". Internet Encyclopedia of Philosophy.
• Cloning Fact Sheet from Human Genome Project Information website.
• 'Cloning' Freeview video by the Vega Science Trust and the BBC/OU
• Cloning in Focus, an accessible and comprehensive look at cloning research from the University of Utah's Genetic Science Learning Center
• Click and Clone. Try it yourself in the virtual mouse cloning laboratory, from the University of Utah's Genetic Science Learning Center
• "Cloning Addendum: A statement on the cloning report issues by the President's Council on Bioethics," The National Review, 15 July 2002 8:45am