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Making Dolly

Dolly was part of a series of experiments at The Roslin Institute that were trying to develop a better method for producing genetically modified livestock. If successful, this would mean fewer animals would need to be used in future experiments. Scientists at Roslin also wanted to learn more about how cells change during development and whether a specialised cell, such as a skin or brain cell, could be used to make a whole new animal.

These experiments were carried out at The Roslin Institute by a team led by Professor Sir Ian Wilmut. Because of the nature of the research, the team was made up of many different people, including scientists, embryologists, surgeons, vets and farm staff.

Dolly was cloned from a cell taken from the mammary gland of a six-year-old Finn Dorset sheep and an egg cell taken from a Scottish Blackface sheep. She was born to her Scottish Blackface surrogate mother on 5 th July 1996. Dolly's white face was one of the first signs that she was a clone because if she was genetically related to her surrogate mother, she would have had a black face.

Because Dolly's DNA came from a mammary gland cell, she was named after the country singer Dolly Parton.
Learn more about cloning with our cloning FAQs.
Why was Dolly so important?

Dolly was important because she was the first mammal to be cloned from an adult cell. Her birth proved that specialised cells could be used to create an exact copy of the animal they came from. This knowledge changed what scientists thought was possible and opened up a lot of possibilities in biology and medicine, including the development of personalised stem cells known as iPS cells.

However, Dolly was not the first ever cloned mammal. That honour belongs to another sheep which was cloned from an embryo cell and born in 1984 in Cambridge, UK. Two other sheep, Megan and Morag, had also been cloned from embryonic cells grown in the lab at The Roslin Institute in 1995 and six other sheep, cloned from embryonic and foetal cells, were born at Roslin at the same time as Dolly. What made Dolly so special was that she had been made from an adult cell, which no-one at the time thought was possible.

Dolly's life

Dolly was announced to the world on 22 nd February 1997 to a frenzy of media attention. The Roslin team chose to make the announcement at this time to coincide with the publication of the scientific paper which describes the experiments that produced her. Dolly captured the public's imagination - no small feat for a sheep - and sparked a public debate about the possible benefits and dangers of cloning.

In the week following the announcement, The Roslin Institute received 3,000 phone calls from around the world.

When Dolly was one year old, analysis of her DNA showed that her telomeres were shorter than would be expected for a normal sheep of the same age. Telomeres are 'caps' on the ends of DNA molecules that protect the DNA from damage. As an animal or person ages, their telomeres become progressively shorter, exposing the DNA to more damage.

It's thought that Dolly had shorter telomeres were because her DNA came from an adult sheep and the telomeres had not been fully renewed during her development. This could have meant that Dolly was 'older' than her actual age. However, extensive health screens on Dolly at the time did not find any conditions which could be directly related to premature or accelerated ageing.

Dolly spent her life at The Roslin Institute and, apart from the occasional media appearance, led a normal life with the other sheep at the Institute. Over the years Dolly had a total of six lambs with a Welsh Mountain ram called David. Their first lamb, Bonnie, was born in April 1998, twins Sally and Rosie were born the following year and triplets Lucy, Darcy and Cotton the year after.

After Dolly gave birth to her last lambs in September 2000, it was discovered that she had become infected by a virus called Jaagsiekte sheep retrovirus (JSRV), which causes lung cancer in sheep. Other sheep at The Roslin Institute had also been infected with JSRV in the same outbreak.

In 2001, Dolly was diagnosed with arthritis after farm staff noticed her walking stiffly. This was successfully treated with anti-inflammatory medication, although the cause of the arthritis was never discovered.

Dolly continued to have a normal quality of life until February 2003, when she developed a cough. A CT scan showed tumours growing in her lungs and the decision was made to euthanise Dolly rather than risk her suffering. Dolly was put to sleep on 14 th February 2003, at the age of six.

Where is Dolly now?

After her death The Roslin Institute donated Dolly's body to the National Museum of Scotland in Edinburgh, where she has become one of the museum's most popular exhibits. Dolly is back on display in the museum after an extensive gallery refurbishment, alongside an interactive exhibit on the ethics of creating transgenic animals featuring current research from The Roslin Institute.
National Museums Scotland blog post - 'Goodbye Dolly'

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Dolly was part of a series of experiments at The Roslin Institute that were trying to develop a better method for producing genetically modified livestock. If successful, this would mean fewer animals would need to be used in future experiments.

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Click and Clone [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2014 [cited 2022 Jan 13] Available from https://learn.genetics.utah.edu/content/cloning/clickandclone/

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Comfortably seated in the fertility clinic with Vivaldi playing softly in the background, you and your partner are brought coffee and a folder. Inside the folder is an embryo menu. Each embryo has a description, something like this:

Embryo 78 - male
No serious early onset diseases, but a carrier for phenylketonuria (a metabolic malfunction that can cause behavioural and mental disorders. Carriers just have one copy of the gene, so don't get the condition themselves).
Higher than average risk of type 2 diabetes and colon cancer.
Lower than average risk of asthma and autism.
Dark eyes, light brown hair, male pattern baldness.
40% chance of coming in the top half in SAT tests.

There are 200 of these embryos to choose from, all made by in vitro fertilisation (IVF) from you and your partner's eggs and sperm. So, over to you. Which will you choose?

If there's any kind of future for "designer babies", it might look something like this. It's a long way from the image conjured up when artificial conception, and perhaps even artificial gestation, were first mooted as a serious scientific possibility. Inspired by predictions about the future of reproductive technology by the biologists JBS Haldane and Julian Huxley in the 1920s, Huxley's brother Aldous wrote a satirical novel about it.

That book was, of course, Brave New World, published in 1932. Set in the year 2540, it describes a society whose population is grown in vats in an impersonal central hatchery, graded into five tiers of different intelligence by chemical treatment of the embryos. There are no parents as such - families are considered obscene. Instead, the gestating fetuses and babies are tended by workers in white overalls, "their hands gloved with a pale corpse‑coloured rubber", under white, dead lights.

Brave New World has become the inevitable reference point for all media discussion of new advances in reproductive technology. Whether it's Newsweek reporting in 1978 on the birth of Louise Brown, the first "test-tube baby" (the inaccurate phrase speaks volumes) as a "cry round the brave new world", or the New York Times announcing " The brave new world of three-parent IVF " in 2014, the message is that we are heading towards Huxley's hatchery with its racks of tailor-made babies in their "numbered test tubes".

The spectre of a harsh, impersonal and authoritarian dystopia always looms in these discussions of reproductive control and selection. Novelist Kazuo Ishiguro, whose 2005 novel, Never Let Me Go, described children produced and reared as organ donors, last month warned that thanks to advances in gene editing, "we're coming close to the point where we can, objectively in some sense, create people who are superior to others ".

But the prospect of genetic portraits of IVF embryos paints a rather different picture. If it happens at all, the aim will be not to engineer societies but to attract consumers. Should we allow that? Even if we do, would a list of dozens or even hundreds of embryos with diverse yet sketchy genetic endowments be of any use to anyone?

I don't think we are going to see superman or a split in the species any time soon, because we just don't know enough

Henry Greely, bioethicist

The shadow of Frankenstein 's monster haunted the fraught discussion of IVF in the 1970s and 80s, and the misleading term "three-parent baby" to refer to embryos made by the technique of mitochondrial transfer - moving healthy versions of the energy-generating cell compartments called mitochondria from a donor cell to an egg with faulty, potentially fatal versions - insinuates that there must be something "unnatural" about the procedure.

Every new advance puts a fresh spark of life into Huxley's monstrous vision. Ishiguro's dire forecast was spurred by the gene-editing method called Crispr-Cas9, developed in 2012, which uses natural enzymes to target and snip genes with pinpoint accuracy. Thanks to Crispr-Cas9, it seems likely that gene therapies - eliminating mutant genes that cause some severe, mostly very rare diseases - might finally bear fruit, if they can be shown to be safe for human use. Clinical trials are now under way.

But modified babies? Crispr-Cas9 has already been used to genetically modify (nonviable) human embryos in China, to see if it is possible in principle - the results were mixed. And Kathy Niakan of the Francis Crick Institute in the UK has been granted a licence by the Human Fertilisation and Embryology Authority (HFEA) to use Crispr-Cas9 on embryos a few days old to find out more about problems in these early stages of development that can lead to miscarriage and other reproductive problems.

Most countries have not yet legislated on genetic modification in human reproduction, but of those that have, all have banned it. The idea of using Crispr-Cas9 for human reproduction is largely rejected in principle by the medical research community. A team of scientists warned in Nature less than two years ago that genetic manipulation of the germ line (sperm and egg cells) by methods like Crispr-Cas9, even if focused initially on improving health, " could start us down a path towards non-therapeutic genetic enhancement ".

Besides, there seems to be little need for gene editing in reproduction. It would be a difficult, expensive and uncertain way to achieve what can mostly be achieved already in other ways, particularly by just selecting an embryo that has or lacks the gene in question. "Almost everything you can accomplish by gene editing, you can accomplish by embryo selection," says bioethicist Henry Greely of Stanford University in California.

Because of unknown health risks and widespread public distrust of gene editing, bioethicist Ronald Green of Dartmouth College in New Hampshire says he does not foresee widespread use of Crispr-Cas9 in the next two decades, even for the prevention of genetic disease, let alone for designer babies. However, Green does see gene editing appearing on the menu eventually, and perhaps not just for medical therapies. "It is unavoidably in our future," he says, "and I believe that it will become one of the central foci of our social debates later in this century and in the century beyond." He warns that this might be accompanied by "serious errors and health problems as unknown genetic side effects in 'edited' children and populations begin to manifest themselves".

For now, though, if there's going to be anything even vaguely resembling the popular designer-baby fantasy, Greely says it will come from embryo selection, not genetic manipulation. Embryos produced by IVF will be genetically screened - parts or all of their DNA will be read to deduce which gene variants they carry - and the prospective parents will be able to choose which embryos to implant in the hope of achieving a pregnancy. Greely foresees that new methods of harvesting or producing human eggs, along with advances in preimplantation genetic diagnosis (PGD) of IVF embryos, will make selection much more viable and appealing, and thus more common, in 20 years' time.

PGD is already used by couples who know that they carry genes for specific inherited diseases so that they can identify embryos that do not have those genes. The testing, generally on three- to five-day-old embryos, is conducted in around 5% of IVF cycles in the US. In the UK it is performed under licence from the HFEA, which permits screening for around 250 diseases including thalassemia, early-onset Alzheimer's and cystic fibrosis.

As a way of "designing" your baby, PGD is currently unattractive. "Egg harvesting is unpleasant and risky and doesn't give you that many eggs," says Greely, and the success rate for implanted embryos is still typically about one in three. But that will change, he says, thanks to developments that will make human eggs much more abundant and conveniently available, coupled to the possibility of screening their genomes quickly and cheaply.

Carey Mulligan, Keira Knightley and Andrew Garfield in the 2010 film adaptation of Kazuo Ishiguro's Never Let Me Go, in which clones are produced to provide spare organs for their originals. Photograph: 20th Century Fox/Everett/Rex

Advances in methods for reading the genetic code recorded in our chromosomes are going to make it a routine possibility for every one of us - certainly, every newborn child - to have our genes sequenced. "In the next 10 years or so, the chances are that many people in rich countries will have large chunks of their genetic information in their electronic medical records," says Greely.

But using genetic data to predict what kind of person an embryo would become is far more complicated than is often implied. Seeking to justify unquestionably important research on the genetic basis of human health, researchers haven't done much to dispel simplistic ideas about how genes make us. Talk of "IQ genes", "gay genes" and "musical genes" has led to a widespread perception that there is a straightforward one-to-one relationship between our genes and our traits. In general, it's anything but.

There are thousands of mostly rare and nasty genetic diseases that can be pinpointed to a specific gene mutation. Most more common diseases or medical predispositions - for example, diabetes, heart disease or certain types of cancer - are linked to several or even many genes, can't be predicted with any certainty, and depend also on environmental factors such as diet.

When it comes to more complex things like personality and intelligence, we know very little. Even if they are strongly inheritable - it's estimated that up to 80% of intelligence, as measured by IQ, is inherited - we don't know much at all about which genes are involved, and not for want of looking.

At best, Greely says, PGD might tell a prospective parent things like "there's a 60% chance of this child getting in the top half at school, or a 13% chance of being in the top 10%". That's not much use.

We might do better for "cosmetic" traits such as hair or eye colour. Even these "turn out to be more complicated than a lot of people thought," Greely says, but as the number of people whose genomes have been sequenced increases, the predictive ability will improve substantially.

Ewan Birney, director of the European Bioinformatics Institute near Cambridge, points out that, even if other countries don't choose to constrain and regulate PGD in the way the HFEA does in the UK, it will be very far from a crystal ball.

Nearly anything you can measure for humans, he says, can be studied through genetics, and analysing the statistics for huge numbers of people often reveals some genetic component. But that information "is not very predictive on an individual basis," says Birney. "I've had my genome sequenced on the cheap, and it doesn't tell me very much. We've got to get away from the idea that your DNA is your destiny."

If the genetic basis of attributes like intelligence and musicality is too thinly spread and unclear to make selection practical, then tweaking by genetic manipulation certainly seems off the menu too. "I don't think we are going to see superman or a split in the species any time soon," says Greely, "because we just don't know enough and are unlikely to for a long time - or maybe for ever."

If this is all "designer babies" could mean even in principle - freedom from some specific but rare diseases, knowledge of rather trivial aspects of appearance, but only vague, probabilistic information about more general traits like health, attractiveness and intelligence - will people go for it in large enough numbers to sustain an industry?

Greely suspects, even if it is used at first only to avoid serious genetic diseases, we need to start thinking hard about the options we might be faced with. "Choices will be made," he says, "and if informed people do not participate in making those choices, ignorant people will make them."

The Crispr/Cas9 system uses a molecular structure to edit genomes. Photograph: Alamy

Green thinks that technological advances could make "design" increasingly versatile. In the next 40-50 years, he says, "we'll start seeing the use of gene editing and reproductive technologies for enhancement: blond hair and blue eyes, improved athletic abilities, enhanced reading skills or numeracy, and so on."

He's less optimistic about the consequences, saying that we will then see social tensions "as the well-to-do exploit technologies that make them even better off", increasing the relatively worsened health status of the world's poor. As Greely points out, a perfectly feasible 10-20% improvement in health via PGD, added to the comparable advantage that wealth already brings, could lead to a widening of the health gap between rich and poor, both within a society and between nations.

Others doubt that there will be any great demand for embryo selection, especially if genetic forecasts remain sketchy about the most desirable traits. "Where there is a serious problem, such as a deadly condition, or an existing obstacle, such as infertility, I would not be surprised to see people take advantage of technologies such as embryo selection," says law professor and bioethicist R Alta Charo of the University of Wisconsin. "But we already have evidence that people do not flock to technologies when they can conceive without assistance."

The poor take-up of sperm banks offering "superior" sperm, she says, already shows that. For most women, "the emotional significance of reproduction outweighs any notion of 'optimisation'". Charo feels that "our ability to love one another with all our imperfections and foibles outweighs any notion of 'improving' our children through genetics".

All the same, societies are going to face tough choices about how to regulate an industry that offers PGD with an ever-widening scope. "Technologies are very amoral," says Birney. "Societies have to decide how to use them" - and different societies will make different choices.

One of the easiest things to screen for is sex. Gender-specific abortion is formally forbidden in most countries, although it still happens in places such as China and India where there has been a strong cultural preference for boys. But prohibiting selection by gender is another matter. How could it even be implemented and policed? By creating some kind of quota system?

And what would selection against genetic disabilities do to those people who have them? "They have a lot to be worried about here," says Greely. "In terms of whether society thinks I should have been born, but also in terms of how much medical research there is into diseases, how well understood it is for practitioners and how much social support there is."

Once selection beyond avoidance of genetic disease becomes an option - and it does seem likely - the ethical and legal aspects are a minefield. When is it proper for governments to coerce people into, or prohibit them from, particular choices, such as not selecting for a disability? How can one balance individual freedoms and social consequences?

"The most important consideration for me," says Charo, "is to be clear about the distinct roles of personal morality, by which individuals decide whether to seek out technological assistance, versus the role of government, which can prohibit, regulate or promote technology."

She adds: "Too often we discuss these technologies as if personal morality or particular religious views are a sufficient basis for governmental action. But one must ground government action in a stronger set of concerns about promoting the wellbeing of all individuals while permitting the widest range of personal liberty of conscience and choice."

"For better or worse, human beings will not forgo the opportunity to take their evolution into their own hands," says Green. "Will that make our lives happier and better? I'm far from sure."

A scientist at work during an IVF process. Photograph: Ben Birchall/PA

Easy pickings: the future of designer babies

The simplest and surest way to "design" a baby is not to construct its genome by pick'n'mix gene editing but to produce a huge number of embryos and read their genomes to find the one that most closely matches your desires.

Two technological advances are needed for this to happen, says bioethicist Henry Greely of Stanford University in California. The production of embryos for IVF must become easier, more abundant and less unpleasant. And gene sequencing must be fast and cheap enough to reveal the traits an embryo will have. Put them together and you have "Easy PGD" (preimplantation genetic diagnosis): a cheap and painless way of generating large numbers of human embryos and then screening their entire genomes for desired characteristics.

"To get much broader use of PGD, you need a better way to get eggs," Greely says. "The more eggs you can get, the more attractive PGD becomes." One possibility is a one-off medical intervention that extracts a slice of a woman's ovary and freezes it for future ripening and harvesting of eggs. It sounds drastic, but would not be much worse than current egg-extraction and embryo-implantation methods. And it could give access to thousands of eggs for future use.

An even more dramatic approach would be to grow eggs from stem cells - the cells from which all other tissue types can be derived. Some stem cells are present in umbilical blood, which could be harvested at a person's birth and frozen for later use to grow organs - or eggs.

Even mature cells that have advanced beyond the stem-cell stage and become specific tissue types can be returned to a stem-cell-like state by treating them with biological molecules called growth factors. Last October, a team in Japan reported that they had made mouse eggs this way from skin cells, and fertilised them to create apparently healthy and fertile mouse pups.

Thanks to technological advances, the cost of human whole-genome sequencing has plummeted. In 2009 it cost around $50,000; today it is most like $1,500, which is why several private companies can now offer this service. In a few decades it could cost just a few dollars per genome. Then it becomes feasible to think of PGD for hundreds of embryos at a time.

"The science for safe and effective Easy PGD is likely to exist some time in the next 20 to 40 years," says Greely. He thinks it will then become common for children to be conceived through IVF using selected genomes. He forecasts that this will lead to "the coming obsolescence of sex" for procreation.

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Designer babies: an ethical horror waiting to happen?

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Nearly 40 years since the first 'test-tube baby', how close are we to editing out all of our genetic imperfections - and should we even try to do so?

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A girl with 3 parents - the beginning of designer babies

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A girl with 3 parents - the beginning of designer babies

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Alana Saarinen loves playing golf and the piano, listening to music and hanging out with friends. In those respects, she's like many teenagers around the world. Except she's not, because every cell in Alana's body isn't like mine and yours - Alana is one of a few people in the world who have DNA from three people.

"A lot of people say I have facial features from my mum, my eyes look like my dad... I have some traits from them and my personality is the same too," says Alana.

"I also have DNA from a third lady. But I wouldn't consider her a third parent, I just have some of her mitochondria."

Mitochondria are often called the cell's factories. They are the bits that create the energy all of our cells need to work, and keep the body functioning. But they also contain a little bit of DNA.

Alana Saarinen is one of only 30 to 50 people in the world who have some mitochondria, and therefore a bit of DNA, from a third person. She was conceived through a pioneering infertility treatment in the USA which was later banned.

But soon there could be more people like Alana, with three genetic parents, because the UK is looking to legalise a new, similar technique which would use a donor's mitochondria to try to eliminate debilitating genetic diseases. It is called mitochondrial replacement and if Parliament votes to let this happen, the UK would become the only country in the world to allow children with three people's DNA to be born.

The structure of a cell

Nucleus: Where the majority of our DNA is held - this determines how we look and our personality

Mitochondria: Often described as the cell's factories, these create the energy to make the cell function

Cytoplasm: The jelly like substance that contains the nucleus and mitochondria

Alana was born through an infertility treatment called cytoplasmic transfer.

Her mum, Sharon Saarinen, had been trying to have a baby for 10 years through numerous IVF procedures.

"I felt worthless. I felt guilty that I couldn't give my husband a child. When you want a biological child but you can't have one, you're distraught. You can't sleep, it's 24-7, constantly on your mind," she says.

Cytoplasmic transfer was pioneered in the late 1990s by a clinical embryologist Dr Jacques Cohen and his team at the St Barnabus Institute in New Jersey, US.

"We felt that there was a chance that there was some element, some structure in the cytoplasm that didn't function optimally. One of the major candidates that could have been involved here are structures called mitochondria," he says.

Cohen transferred a bit of a donor woman's cytoplasm, containing mitochondria, to Sharon Saarinen's egg. It was then fertilised with her husband's sperm. As a little bit of mitochondria was transferred, some DNA from the donor was in the embryo.

Seventeen babies were born at Cohen's clinic, as a result of cytoplasmic transfer, who could have had DNA from three people.

But there was concern about some of the babies.

"There was one early miscarriage, considering there were twelve pregnancies that is an expected number," says Cohen.

He and his team believed that miscarriage occurred because the foetus was missing an X chromosome.

"Then there was another twin pregnancy, where one [of the twins] was considered entirely normal and the other had a missing X chromosome.

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"So that's two out of the small group of foetuses that was obtained from this procedure. This did worry us and we reported that in the literature and in our ethical and review board that oversees these procedures," he says.

At the time of birth, the other babies were all fine. A year or two later, another of the children was found to have "early signs of pervasive early developmental disorder which is a range of cognitive diseases which also includes autism." Cohen told me.

He says it's difficult to know if the abnormalities happened by chance or because of the procedure.

Other clinics copied the technique and Cohen estimates that around 30 to 50 children worldwide were born who could have DNA from three people as a result.

But in 2002 the American regulator, the FDA (Food and Drug Administration) asked clinics to stop doing cytoplasmic transfer due to safety and ethical concerns. All of them did.

"There was a reaction from scientists, ethicists, the public at large, I think most of it was supportive, some of it was critical - I think this is normal, every time an experiment is done in medicine there is a reaction - what are the risks here?" says Cohen.

At the time, some were concerned because they felt this was germ line genetic modification. What "germ line" means is that a child like Alana would pass her unusual genetic code down to her children. And their children, would pass it to their children and so on.

Because we inherit our mitochondria only from our mothers, only female children would pass their unusual genetic code on. Crossing the germ line as it is known has never been done before so very little is known about what the outcome could be.

Due to a lack of funding, Cohen says, it hasn't been possible to find out about how any of the children like Alana who were born from cytoplasmic transfer are doing. But the St Barnabus Institute is now starting a follow up study to check their progress.

Sharon Saarinen says her daughter Alana is a healthy, typical teenager

"I couldn't ask for a better child. She is an intelligent, beautiful girl inside and out, she loves math and science ... she does really well in school. She helps me around the house... when she's not texting!"

"She has always been healthy. Never anything more than a basic cold, or a flu every now and then. No health problems at all."

The health of the children, like Alana, born from cytoplasmic transfer is under scrutiny now because of the UK's decision to consider legalising mitochondrial replacement, where the mitochondria of a donor woman will be used to create a child.

It would not be available for people with fertility problems but for those who carry diseases of the mitochondria and would otherwise pass down these genetic abnormalities to their children.

Exactly how it is done still needs to be determined as there are two ways of doing the procedure, depending on when the eggs are fertilised.

Eggs from a mother with unhealthy mitochondria and a donor with healthy mitochondria are collected

The nucleus, containing the majority of the genetic material, is removed from both eggs. The donor nucleus is destroyed

The mother's nucleus is inserted into the donor egg - it now has healthy mitochondria. The egg is then fertilised by the father's sperm

Both the mother's and donor's eggs are fertilised with the father's sperm to create two embryos

The pronuclei, the nuclei during the process of fertilisation, contain the majority of the genetic material. They are removed from both embryos. The donor's is destroyed

A healthy embryo is created by putting the parents' pronuclei into the donor embryo

"Mitochondrial diseases tend to involve tissues or organs which are heavily dependent on energy," says Prof Doug Turnbull from The University of Newcastle. He has treated people with mitochondrial disease for decades and is one of those who has developed these new techniques to try to cure these debilitating diseases.

"The conditions can therefore involve the heart, the brain or sometimes the skeletal muscle," he says.

"People can have very bad heart problems which can cause the heart to fail eventually, they can be very weak and require respirators or be in a wheelchair. With the brain, they can get epilepsy, strokes and eventually severe dementia."

Turnbull estimates that around 1 in 3000-5000 people in the UK have a mitochondrial disease. "We can treat the symptoms. We can improve the quality and length of peoples' lives but we can't cure them."

The mitochondria carry some DNA, around 13 "important genes" says Turnbull.

That compares to the "23,000 important genes" in the nucleus where most of our DNA is held. This is the DNA that determines our traits and personality.

"We're not trying to create some characteristic that makes this person a stronger person or [someone who] will have blonde hair. We're trying to prevent disease and I think that is the only justification for doing this," he says.

Sharon Bernardi, from Sunderland in the North of England, is someone who mitochondrial replacement could have helped.

Bernardi has lost seven children to mitochondrial disease.

I have to slip back into reality and think don't be silly, Edward's not there. He's not in his room
Sharon Bernardi

"I have babies in three different cemeteries," she told us in her sitting room, surrounded by photographs of all her children.

"That is not the way you plan your life when you're trying to have a family. I have lovely photos and lovely memories but obviously that's all I have got now."

The doctors didn't know why Bernardi's babies kept passing away only hours after they were born. So that's why she kept trying, hoping she would have a healthy child.

With her fourth child, Edward, at first everything seemed different. He was healthy until he was about four and a half. But it was then that he was diagnosed with Leigh's disease, a type of mitochondrial disease, and his health deteriorated throughout the years.

"From the age of 20 Edward [found] getting around more difficult. He started to get new symptoms - spasms. He'd start screaming... four, five, six hours at a time. His muscles used to tense up, his hands, his face. It was like dystonic spasms - a really bad spasm. [For] eight hours he'd be in pain, screaming. His face would twist up and his hands would get really stiff. It was hard to see."

Edward Bernardi passed away three years ago, when he was 21.

"My life was totally for Edward. Even now sometimes if I have gone to sleep, I still wake up, and think, 'It's very quiet.' I have to slip back into reality and think, 'Don't be silly, Edward's not there. He's not in his room'."

"Without a heartbeat I would have gone for this [mitochondrial replacement]. I hope this is a new option. I hope people take it seriously and it's approved.

"I don't want my son to have just died for nothing. I want him to have made a difference."

"His life was robbed at 21. We're trying to stop this. People have to understand this is a life disease. We're trying not to pass it on to children and make it better for future families."

But some people believe this technique could set us on a slippery slope towards genetically modified humans.

"These regulations would authorise the crossing of a rubicon for the first time. It would authorise germ line therapy... to alter the genes of an individual. This is something defined by the EU Charter of Fundamental Rights as effectively constituting eugenics," says British MP Fiona Bruce who chairs the All Party Parliamentary Pro-Life Group.

There have been few episodes I'm aware of in the history of assisted reproduction that have had to be stopped because of hazard
Professor Braude, Kings College London

"We will have approved a technique and what that technique could be used for in the future who knows. We're opening a Pandora's box."

The regulator in the UK, the HFEA or Human Fertilisation and Embryology Authority, has held three independent reviews to scrutinise the safety of this technique. The conclusions were that mitochondrial replacement is "not unsafe".

That means "it would be reasonable, with some additional experiments, to take it into clinical practice if all circumstances are fulfilled" says Peter Braude, emeritus professor of obstetrics and gynaecology at Kings College London. He sat on all three HFEA scientific reviews.

"In any move from science to clinical practice there is a leap of faith - it has to be done," he says.

He adds that many of the concerns being raised now about this are the same as the ones cited in the early days of IVF. The UK has for decades been a leader in assisted reproduction science and is where the world's first test tube baby, Louise Brown, was born in 1978.

"The headlines then were 'playing God' and 'genetically modified humans'," says Braude.

"There have been few episodes I'm aware of in the history of assisted reproduction that have had to be stopped because of hazard. It's all gone pretty swimmingly as far as I'm aware."

Braude says that mitochondrial replacement has gone through much more scrutiny than previous, now well established, assisted reproduction techniques did, such as IVF.

"Whereas the original techniques were used with only [experiments from] mice, rabbits, lab animals... the big difference here is we also have issue of human embryos and this work has been tested in macaque monkeys in primates. All those were very useful, reassuring... hence why we came to the conclusion that this is not unsafe."

The experiments done on macaque monkeys were done in Oregon, US and the monkeys are now five years old and seem to be healthy.

Braude also points out that having a third person's DNA in your system is "nothing particularly new".

"Think about bone marrow transplants, let's say unfortunately you have leukaemia and you have to have your bone marrow radiated for the cancer to be killed and then it is replaced by bone marrow from someone else - say me. Effectively from that time onwards, you will have circulating in your body DNA from me. You won't be related to me, you may be grateful to me, but you will have DNA from a third person circulating in your body."

What is different, say critics, about mitochondrial replacement, is that DNA from the donor will be passed down future generations.

Dr Ted Morrow, an evolutionary biologist from the University of Sussex, and colleagues have carried out mitochondrial replacement experiments on other animals. He raised safety concerns about mitochondrial replacement to the scientific reviews.

"For mice, there were changes in cognitive ability... to learn and do things using their brain. In fruit flies and seed beetles there were changes in male fertility, changes in ageing, a range of different traits were effected in various experiments," he says.

I'm a scientist but I'm not a pro-lifer. I think this is a genuine safety concern - that's it
Ted Morrow, University of Sussex

The HFEA's scientific reviews dismissed Morrow's findings as not relevant to humans because they were done on inbred animals.

Morrow stands by his research and says the scientific panels should not have dismissed his findings so quickly.

It is Morrow's evidence that critics such as Fiona Bruce cite when saying this technique is not safe enough.

She has called a debate in the House of Commons today to discuss mitochondrial replacement. She does not believe there has been enough debate about what the UK is proposing to do. "The technique itself could allow the child to inherit untried untested medical complications," she says.

Morrow says that all the coverage of his research has been "a rather odd experience".

"In the press it's sometimes portrayed that the scientists think this, and the pro-life group this. I'm a scientist but I'm not a pro-lifer. I think this is a genuine safety concern - that's it."

Alana and Sharon Saarinen have been watching the debate in the UK with interest.

"I wish I could meet her, the donor, to tell her I am so grateful for what she did for us. How can you thank someone for giving you a life? That's impossible," says Sharon.
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Alana agrees with her mum. "I think it would be nice to thank her. But I wouldn't want to have a relationship or connection with her. The DNA I have of her is just so small."

"I know she might have another person's mitochondria, [but] look what a great person she turned out to be, and healthy. Just because she'll pass it on to her children it won't bother me in the least. I know it was the right thing to do. I have the living proof every day to see how great it turned out."

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Alana Saarinen loves playing golf and the piano, listening to music and hanging out with friends. In those respects, she's like many teenagers around the world. Except she's not, because every cell in Alana's body isn't like mine and yours - Alana is one of a few people in the world who have DNA from three people.

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Regulations and policies change frequently to keep up with the pace of research, as well as to reflect the views of different political parties. Here President Obama signs an executive order on stem cells, reversing some limits on federal research funding. (White House photo by Chuck Kennedy)

Governments around the globe have passed legislation to regulate stem cell research. In the United States, laws prohibit the creation of embryos for research purposes. Scientists instead receive "leftover" embryos from fertility clinics with consent from donors. Most people agree that these guidelines are appropriate.

Disagreements surface, however, when political parties debate about how to fund stem cell research. The federal government allocates billions of dollars each year to biomedical research. But should taxpayer dollars be used to fund embryo and stem cell research when some believe it to be unethical? Legislators have had the unique challenge of encouraging advances in science and medicine while preserving a respect for life.

U.S. President Bush, for example, limited federal funding to a study of 70 or so hES cell lines back in 2001. While this did slow the destruction of human embryos, many believe the restrictions set back the progress of stem cell research.

President Obama overturned Bush's stem cell policy in 2009 to expand the number of stem cell lines available to researchers. Policy-makers are now grappling with a new question: Should the laws that govern other types of pluripotent stem cells differ from those for hES cells? If so, what new legislation is needed?

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Governments around the globe have passed legislation to regulate stem cell research. In the United States, laws prohibit the creation of embryos for research purposes. Scientists instead receive "leftover" embryos from fertility clinics with consent from donors. Most people agree that these guidelines are appropriate.

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This page has content that requires the Flash Player plug-in. Unfortunately, we can't do anything on our end to improve your experience with Flash. If you are using an iOS device, please note that these devices do not support Flash. We are slowly working on replacing our popular Flash-based content and will update this content as it becomes available.