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The idea of human cloning was science fiction when it was first imagined. But in the last few decades, technological and scientific advances have made this a real possibility. Although the ethics of cloning a human are questionable, the technology has led to some promising reproductive and health therapies.

The most basic definition of cloning is the creation of an exact genetic copy of an organism, tissue, cell or gene, according to the U.S. National Library of Medicine. The how and why of cloning really depends on what is being cloned. There are three main types of cloning: Gene cloning, reproductive cloning and therapeutic cloning.

Related: How stem cell cloning works (infographic)

The most commonly applied type of cloning is gene cloning. At its most basic, gene cloning is a biochemical reaction that takes place in every single cell in every organism. It's the creation of a copy of genetic material from an existing strand of genetic material. This natural reaction can be recreated in the lab and is an essential tool for many aspects of biological research.

The most commonly discussed and debated type of cloning is reproductive cloning. This type of cloning creates genetic duplicates of whole organisms from the genetic material of an already-existing organism. A cloned organism is very similar to being an identical twin to the parent organism, just born later.

And perhaps the most medically applicable type of cloning for humans is therapeutic cloning, which creates cloned embryonic stem cells of a patient to create genetically identical cells that can treat a medical condition. "Therapeutic cloning refers to the use of embryonic stem cells that in our lab we derive from somatic cells from a patient's skin," Shoukhrat Mitalipov, an embryologist at Oregon Health & Science University in Portland, told LiveScience in an email. "In our research lab we can develop [these cells] into different kinds of cells in the body such as neurons or cardiovascular cells."

Yes, cloning is real, but it may not look like it does in science fiction stories.

Some types of cloning occur in nature regularly. For example, bacteria can reproduce asexually, essentially cloning themselves all the time. Similarly, parthenogenesis is a unique biological phenomenon that results in the spontaneous creation of natural clones it happens in some species of sharks, amphibians, lizards and snakes. In humans, every cell in the body is a clone of the first embryo cell created when the father's sperm fertilized the mother's egg, and identical twins are natural clones.

Related: Rare 'virgin birth' of shark in Italian aquarium could be first of its kind

Cloning is also very real in the biology lab researchers worldwide use gene cloning in many ways. For example, it can create large amounts of proteins for medications like insulin or be used to detect the presence of specific strands of DNA, like in the COVID-19 PCR test.

It has been more than a quarter of a century since researchers first cloned animals from adult cells. The most well-known animal clone is Dolly the sheep, created in 1996 at the University of Edinburgh. While not the first cloned mammal, Dolly was the first created from an adult cell, rather than an embryonic or fetal cell.

To create Dolly, researchers needed to clone 277 embryos, 29 of those were healthy enough to implant, but only one survived until birth. In those early years, cloned embryos faced many failures, and the animals born alive sometimes died prematurely. According to the National Human Genome Research Institute, sheep and other cloned mammals have had various organ defects, including the heart, brain and liver. Other reports suggest issues with premature aging, increased birth size and immune system issues.

Related: 20 years after Dolly the sheep, what have we learned about cloning?

The success of Dolly brought a flurry of media attention to cloning both its potential benefits and the world's fears. As a result, many countries rushed to ban cloning of all kinds.

Nevertheless, in the decades since Dolly, animal cloning has come a long way. Some services will clone pets, as Barbra Streisand had done with her pet, Smithsonian Magazine reported. Some companies will even clone an entire polo team. Polo team La Dolfina, and world-class player Adolfo Cambiaso, have for several years used cloned horses, according to a 2016 article in Science magazine.

Related: Cloning mammoths is still a dream.

The work to clone other animals has been a slow, uphill battle but over the past few decades, researchers have been working their way toward cloning humans.

In 2007, Mitalipovs research team cloned the first primate embryos rhesus macaque and used them to create embryonic stem cells, publishing the process in the journal Nature. But it took until 2018 for these technologies to result in a living cloned monkey, achieved by a team of Chinese scientists and described in their paper published in the journal Cell, Live Science previously reported. The researchers made about 80 cloned embryos, ending up with six pregnancies and just two live births.

Six years after cloning the monkeys, Mitalipovs team created embryonic stem cells from cloned human embryos, research he published in 2013 in the journal Cell. At this point, many of the technologies needed to create human clones exist, but there are still many roadblocks and ethical arguments against using them to clone a human.

As cells grow and divide, they naturally create clones using cellular division, a process called mitosis. The cells use proteins and enzymes coded in their genes to copy their genetic material. As researchers developed an understanding of how cells reproduce their genes, scientists began recreating these reactions in the lab. Now, cloning genes in the lab is as easy as mixing a drink combining the proteins that cells use to copy their DNA and adding a gene to copy.

"Cloning DNA or cells is simple; it's the nature of DNA to replicate itself," Mitalipov said. "But when we say cloning of an entire organism, that's much more complex."

Most multicellular organisms replicate themselves through sexual reproduction. This process takes half of the genetic code from one organism (an egg) and half from another (a sperm). It remixes them, creating a single cell that can turn into a whole new being an embryo that might grow into a new organism if it implants in the right uterus.

But the goal of cloning is to create an embryo without remixing the genome. To do this, the researchers first start with a body cell, called a somatic cell. Somatic cells make up the majority of the body the skin, internal organs, brain cells. A somatic cell's genome has been "set" like jello into a specific shape.

Differences in the structure of somatic cell DNA dictate what genes the cell can express, according to the U.S. National Libraries of Medicine. The differences in gene expression, dictated by chemical changes called epigenetic modifications, determine how the cell looks, how it acts, and what it does in the body. And that process is limiting that cell then can't do anything else in the body. It will just age and die, and be broken down into parts to be reused.

Embryonic cells, or stem cells, on the other hand, have the potential to become any type of cell in the body because the genes they can express aren't locked in like they are in somatic cells. Researchers use both types of cells to create clones. The process originally used to create Dolly the sheep is called somatic cell nuclear transfer, as described in a 2015 review in the journal Philosophical Transactions of the Royal Society B. In this process, scientists remove the nucleus, or genetic hub, of a somatic cell and insert it into an egg cell that has had its genome removed.

If successful, this process will reset the somatic genome's epigenetics, and result in a cloned embryo with an exact copy of the genome of the somatic cell without the epigenetic modifications. It sounds straightforward, but the process is incredibly finicky to be successful the egg needs exactly the right conditions, and these conditions differ with every species. So, when scientists attempt to clone a new animal, they're faced with making many adjustments to the general process, Mitalipov said.

"You'd have to resolve lots of mysteries and there's no standard protocol to do it," Mitalipov said. "Everything needs to be tweaked a little bit depending on the difference in species."

These might have to do with the chemical environment (including the presence of caffeine in the petri dish for human embryos) that the experiment is performed in, the application of a jolt of electricity, the timing of the steps and even how forcefully the embryo is touched while removing and inserting the somatic cell nucleus.

In his 2013 Nature paper, Mitalipov and his colleagues showed that they had found the conditions to successfully clone a human somatic cell into an embryo, which was then used to create a human embryonic stem cell line.

Following the Mitalipov team's breakthrough in 2013, and the first cloned primates in 2018, the world has been waiting to see if anyone would actually clone a human. But this hasn't happened yet.

But is it possible? The short answer is likely yes. The technology exists and there's nothing significantly different about how human genes or genetics work compared with those of other animals that have been cloned. But, based on the difficulties experienced in developing cloned animal embryos into living, full-term births, there's no saying what types of conditions or diseases a human clone might have if one was born. We also know that it would likely require creating many many embryos to get one live birth a very ethically murky proposition.

Related: Artist's 'cloning agency' replicates Jesus, Lady Gaga

Additionally, humans (and other animals) are more than their DNA. The environment human bodies and brains are exposed to in the womb, during development and extending through childhood and young adulthood, plays a big part in creating who a person is. And just as epigenetic modifications alter how genes are expressed to create specialized somatic cells, they also reflect the things cells and bodies have gone through adding another major layer of complication into the question.

families, many others believe this kind of research is ethically problematic.

The creation and destruction of human embryos is a sticking point for many major religions, and others worry about the potential diseases and conditions that this process might inflict on a cloned baby.

Related: Human cloning? Stem cell advance reignites ethics debate

For these reasons and more, many countries and U.S. states have put bans on human cloning experiments. In the U.S., there are no federal laws against cloning humans, but multiple states have laws prohibiting cloning for any purpose. Multiple others prohibit funding of human cloning. According to intellectual property attorneys Knobbe Martens, 10 states allow the creation of human cloned embryos but prevent them from being implanted researchers can destroy them to create embryonic stem cell lines.

The use of three-parent IVF is illegal due to a 2015 amendment introduced by Rep. Robert Aderholt, a Republican from Alabama, to the 2016 appropriations bill. The amendment forbade clinical trials of heritable genetic modifications. However, patients and scientists are pushing to change that, according to STAT News.

More than 30 countries ban human cloning experiments, according to a 2007 review published by Rice University. In 15 countries, there are bans on human reproductive cloning but not on the creation of cloned embryonic stem cells. Other countries do not have any specific legislation banning human cloning.

While polo ponies are no doubt important to some, there are several other ways that technologies developed through these cloning experiments may be important in the future, Mitalipov said.

Mitalipov's work on somatic cell nuclear transfer in humans has led directly to the development of reproductive technologies that allow women with mitochondrial diseases (which these women pass down to offspring through their eggs) and infertility issues to have healthy children that are genetically related to them. Previously, women with mitochondrial diseases had no recourse other than to pass their condition on or not have biological children.

Now, technology developed by Mitalipov's lab is used to strip donor eggs of their DNA and move the nucleus from the mother's egg, resulting in a healthy embryo that is genetically related to the mother, according to a 2014 review in the journal Fertility and Sterility. Multiple "three-parent babies" have been born using these methods at clinics in the Ukraine and Greece, according to STAT News.

Related: Prenatal genetic screening tests: Benefits & risks

The ability to create cloned embryonic stem cells using somatic nuclear transfer is also promising for developing therapies that a patient's immune system wouldn't reject. These clonal stem cell therapies could create new organs or cells for people that could replace damaged ones.

"You can theoretically use those cells to treat a patient with a neurodegenerative disease or a cardiovascular disease," Mitalipov said. These cells "could, in theory, lead to the development of stem cell therapies treating neurodegenerative diseases like Parkinson's, cardiac disease and spinal cord injuries."

The cloned stem cells can be created now, but there are roadblocks on the research and clinical end to developing these therapies.

"Unfortunately, no therapies have been developed yet," Mitalipov said. "We can grow neurons in a petri dish, but how do you integrate neurons into the brain or other types of cells into relevant organs like the heart? It's going to be very difficult."

In the future, Mitalipov hopes that some of the technologies he's working on now can help create genetically related babies for same-sex couples or infertile couples. For example, his lab is currently figuring out how to remove half of the DNA from a cloned embryonic cell to create an egg cell.

If researchers create a cloned egg cell from the somatic cells of a man or infertile female, it could then be fertilized with the sperm from another man, creating an embryo. Using the cloning technology this way would give same-sex or infertile couples a way to have genetically related babies.

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How does cloning work? | Live Science

It was a glorious day in the hills above Edinburgh, Scotland, when old friends and scientific colleagues Ian Wilmut and Alan Trounson set off on a hike two decades ago. High over the city, Wilmut confided that he had a secret to share. As part of a larger study, he and several co-workers had successfully birthed a lamb in the labnot from egg and sperm but from DNA taken from an adult sheeps mammary gland. They had cloned a mammal. Crikey, I was stunned, says Trounson, who is nowas thena stem cell biologist at Monash University in Melbourne, Australia. He remembers sitting down hard on a nearby stone. It was a warm day but Trounson felt a chill pass over him as he realized the implications. It changed everything.

Cloning a mammal defied the scientific dogma of its time. The success led to dire and fantastic predictions: Humans would be cloned. Diseases would be prevented. Lost children rebirthed. Today, two decades after Dollys birth on July 5, 1996, the impact of cloning on basic science has surpassed expectations whereas the reality of what is technically called nuclear transferthe form of cloning used with Dollyhas largely faded from public consciousness.

In 2016 cloning a person remains unfeasible, with no scientific benefit and an unacceptable level of risk, several scientists say. Most know of no one even considering the feat. And the cloning of animals remains limitedalthough it is likely growing. Some agricultural cloning is used in the U.S. and China to capitalize on the genes of a few extraordinary specimens, scientists say, but the European Parliament voted last year to ban cloning animals for food. One scientist in South Korea charges $100,000 to clone pets, although the level of demand for the service is unclear.

Clonings biggest impact, several researchers say, has been in the stem cell advances it has sparked. Stem cell biologist Shinya Yamanaka said via e-mail that Dollys cloning motivated him to begin developing stem cells derived from adult cellsan accomplishment that won him a Nobel Prize in 2012. Dolly the Sheep told me that nuclear reprogramming is possible even in mammalian cells and encouraged me to start my own project, wrote Yamanaka, who splits his time between the University of California, San Francisco, and the Center for iPS Cell Research and Application (CiRA) at Kyoto University in Japan, which he directs. He used adult cellsfirst in mice, although the technique is now feasible in human cellsto make stem cells that can form a wide range of other cells, essentially turning their cellular clocks back to infancy so they could mature into different adults. Because they are artificially created and can have a variety of futures, they are called induced pluripotent stem (or iPS) cells. The rise of these iPS cells has reduced the need for embryonic stem cellswhich have long caused ethical concerns for someand iPS cells now form the basis for most of todays stem cell research.

Dollys birth was transformative because it proved that the nucleus of the adult cell had all the DNA necessary to give rise to another animal, says stem cell biologist Robin Lovell-Badge, head of the Division of Stem Cell Biology and Developmental Genetics at the Francis Crick Institute in London. Previous researchers had derived adult frogs from embryonic frog cells or embryonic frog cells from adultsat which point their development stalled. Dolly was the first example of taking an adult cell and getting an adult, Lovell-Badge says. That meant you could reprogram an adult cell nucleus back to an embryonic stage.

Dolly died on February 14, 2003, at age six from a lung infection common among animals who are not given access to the outdoors. It probably had nothing to do with her being a cloned animal, says Wilmut, now an emeritus professor at the The Roslin Institute at the University of Edinburgh where he did his initial work.

The sheep, made from breast cells, was famously named after Dolly Parton, the American singer known for her large chest as well as her voice. It wasnt meant to be disrespectful to the lady in question or to women in general, Wilmut said recently, of the name suggested by a stockman. Rather, it helped humanize a research project that might otherwise have seemed detached from everyday life. Science and its presentation can sometimes look terribly serious, he said. I think it was good for usit made us look human.

Wilmut admits Dollys birth was a lucky accident. He and his colleagues were trying to make clones from fetal cells and used adult ones as experimental controlsnot expecting that they would actually generate an embryo of their own. We didnt set out to clone adult cells. We set out to work withideallyembryonic stem cells or things like that, Wilmut says. Being successful with adult cells was a very considerable, unexpected bonus.

The initial aim of the research was to use an animals milk production system as a factory of sorts, manufacturing proteins to treat human diseases. But interest in that idea has declined with the rise of inexpensive synthetic chemicals.

Wilmut says he thinks it would be possible to clone a humanbut highly unadvisable. The cloning technique used to create Dolly has been shown not to work in primates. He believes it could be possible using other techniques but said he is vehemently opposed to the idea of cloning a person. Just because it may now work in the sense of producing offspring doesnt mean to say we should do it, he says. The likelihood is you would get pregnancy losses, abnormal births. For example, one of the lambs his lab cloned soon after Dolly developed lung problems that caused it to hyperventilate and regularly pass out. It was distressing enough to see that in an animal, he says. I wouldnt want to be the person who looked a cloned child in the face and said very sorry. With recent advances in gene-editing technology, the need for cloning to correct genetic errors will decline even further, he notes. Theres even less reason for doing it now than before..

Trounson says he believes there is a large market for cloned livestock embryos. Its pretty busy out there, kind of surprisingly and below the surface, he says. The benefits genomically for production excellence and driving up production parameters is very good, adds Trounson, who recently stepped down after six years as president of the California Institute for Regenerative Medicine, a state agency that provides loans and grants for stem cell research. Thats probably the driver that has kept companies doing it in the U.S.

The U.S. government decided in 2008 that there were no discernable differences between cloned and noncloned cows, goats and pigs, so it allowed the process in those animals, although mainly for breeding rather than meat production. In China a company called Boyalife Group has plans to produce at least 100,0000 cloned beef cattlea fraction of the total number of animals slaughtered each year in that country, a company spokesperson wrote via e-mail. We might be at the best time to advance this technology into applications from both a technology perspective and from a market perspective [in China].

Theoretically, cloning could also be used to bring back endangered species. There has been talk of using it to restore woolly mammoths, giant pandas and even Neandertalsideas Lovell-Badge dismisses as fairly silly. Trounson says he still has a stash of skin samples from critically endangered northern hairy-nosed wombats stored in liquid nitrogen, in case someone ever wants to attempt to restore the speciess numbers. Clones, however, are created by taking an adult cell and fusing it to a recipient egg cell. Making a clone requires an intact nucleus, which would not be available for most extinct species.

Several researchers are now using cloning techniques to produce embryonic stem cells, thereby avoiding the need to collect new embryos. So-called somatic cell nuclear transfer may help researchers better understand early human embryogenesis and stem cell biology, according to Paul Knoepfler, a biologist at the University of California, Davis, who is not directly involved in the work. Knoepfler wrote via e-mail that he does not see any imminent therapeutic benefit [to that work], but that could change in the future.

The idea of cloning a deceased loved onehuman or pethas fallen out of favor in part because of the recognition that environment affects behavior. The genetics might be the same but would a clone still be the same lovable individual? Youre never going to get Tibble back, or whatever, Lovell-Badge says, noting that he thinks the idea of cloning a pet is stupid. He adds, The only possible use that I can sort of vaguely think of is if you have a particular valuable dog, with skills like super-sniffing that scientists would want to determine was inborn or behavioral.

Lovell-Badge is even more dismissive of the idea of cloning a person. Wed have to know an awful lot more about reprogramming and how to make it 100 percent efficient, he says. I have never thought of a good enough reason for a human being.

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20 Years after Dolly the Sheep Led the WayWhere Is Cloning Now?