A clone is a living organism (such as a plant or animal), which shares the same genetic information as another organism. However, their characteristics can be affected by random mutations which occur in their DNA during development in the womb or by the environment that they grow up in, so, although clones have the same DNA, they may not look the same or behave in the same way.
While some clones can be found in nature (see FAQs 6 & 7), it is also possible for scientists to create a clone or identical copy of an organism. It is important to understand that a cloned animal is not the same as a genetically modified animal. A cloned animal shares the same DNA as another animal, while a genetically modified animal has had a change made to its DNA, but does not share its DNA with any other animals.
Scientists can also use bacteria or viruses to replicate or clone individual DNA sequences that they are interested in. This is known as molecular or DNA cloning.
Dolly the Sheep was created using a cloning method called Somatic Cell Nuclear Transfer or SCNT. In SCNT, the nucleus of an egg cell is removed and replaced with the nucleus of a donor adult cell. Because 99.9% of the cell’s DNA is contained in the nucleus as chromosomal DNA (with the remaining 0.1% of DNA found in mitochondria), the resulting animal will share almost exactly the same DNA as the original donor cell.
We do not clone animals any more, mainly because of the low success rate of the technique (Dolly was the only animal born from 277 cloned embryos). In the years since Dolly was born new technologies have been developed, which are vastly more efficient than cloning. However, we still use the skills and experience we gained while working on Dolly in our work with livestock animals today.
Cloned embryos are more likely to be lost during pregnancy than normal embryos, which accounts for the low success rate of cloning. Large Offspring Syndrome (LOS) can also affect some cloned animals. Animals with LOS have growth defects and are considerably larger at birth than animals resulting from natural matings. LOS is more often found in cloned animals from livestock species, such as sheep, than in other cloned animals.
These abnormalities may be caused by the conditions used to grow the cells and embryos in the lab, which might be improved by future research.
Because Dolly’s DNA came from a six year old sheep, there were many questions about whether the cloning process had successfully reset the DNA to that of an embryo or whether Dolly carried artefacts in her DNA that would normally be found in an older animals. This led to speculation about what Dolly’s ‘genetic’ age was and whether she aged more quickly than a sheep that wasn’t a clone. Because Dolly was the first animal to be cloned from an adult cell, scientists did not fully know what happened to the donor DNA during cloning.
Analysis of Dolly’s DNA when she was one year old showed that the protective caps on the end of her chromosomes (known as telomeres) were shorter than those of a normal sheep of the same age. Telomeres get shorter with age and it is possible that Dolly’s telomeres had not been fully renewed during the cloning process. However, the telomeres of other cloned animals have been found to be a similar length or even longer than those of normal animals. The reasons for these differences in telomere length are not completely clear and require further investigation.
Dolly did develop arthritis at the age of four, which could have been a sign that she was ageing prematurely. However, it is not clear whether the arthritis was caused by Dolly’s ‘old’ DNA or by the fact that, for security reasons, she spent a lot of her time in a shed with a concrete floor or that she was given a lot of treats in order to get her to pose for photographs and, as a result, was quite overweight.
Animal cloning for the purposes of scientific research is legal in the European Union, which includes the UK. Like all experiments which involve the use of animals, researchers who want to make cloned animals must have their work approved by the Home Office before they can begin.
In September 2015 the EU voted to ban the cloning of animals for non-research purposes, such as cloning valuable farm animals or pets.
Yes, everywhere! Any organism which can produce offspring on its own, without any other individual being involved, is producing clones. This is also known as reproducing asexually. An example of this are bacterial cells, which reproduce simply by dividing in two. The resulting ‘daughter cells’ share the same DNA as the original bacterium. Some insects such as aphids can reproduce asexually, a process known as parthenogenesis, and all of the offspring are clones of the mother. Many plants can also make clones – if you’ve ever taken a cutting from a plant and grown it, you’ve been cloning!
In a sense, yes. Identical twins occur when a single fertilised egg is split into two, with the two resulting eggs sharing the same DNA. In a sense, they are even more identical to each other than a clone would be to its DNA donor, as they often share the same environments both before and after birth, which clones generally do not.
It is possible that cloning could be used to produce animals from species that are either endangered or extinct, but there are several practical problems which would first have to be solved.
The low efficiency of cloning means that a lot of healthy cells and embryos would be needed to be sure of success. Finding enough cells from an endangered or extinct species as well as a suitable source of recipient egg cells and surrogate mothers poses a considerable challenge. For example, if you wanted to bring dinosaurs back to life, which animal would you use to give birth to the first clones? Another issue is that cells and embryos from different species require very specific conditions to be successfully grown in the lab, if they can be grown at all. Working out what these conditions are can take a lot of time and research – it took four years of further work after Dolly’s birth for pigs to be successfully cloned.
The cloning of farm animals for commercial reasons is allowed in some countries, such as the US, but was banned in the EU in September 2015. Even in countries where commercial livestock cloning is allowed, the high costs mean that generally only animals which are very valuable are cloned. Only the offspring of these cloned animals enter the food chain, although there is growing evidence to suggest that cloned animals are safe for humans to eat.
It is understandable that someone would want to clone a beloved pet after it dies. However, there would still be significant differences between the clone and the original pet, both in their looks and personality. A good example of this is the first cloned cat CC and her DNA donor Rainbow. Although CC is Rainbow’s clone and shares her DNA, the two cats look completely different. This is because coat colour and pattern is influenced by the environment in the womb, something which cannot be replicated by cloning.
It is technically possible to clone humans using the same method which made Dolly. However, following the debate surrounding Dolly’s birth, human cloning for the purposes of producing more humans (reproductive cloning) has been banned in many countries around the world, including the UK. There have been some claims in the media of successful human reproductive cloning, but no scientific evidence has been produced to support these claims.
When Dolly the Sheep was unveiled to the public, many concerns were raised about the possibility of using the same technology to clone humans. The scientists who were involved in the research which produced Dolly have discussed the ethical implications of her birth in many places, from scientific conferences to media interviews and public events, and have repeatedly stated their opposition to human reproductive cloning. In the days following the announcement of Dolly’s birth to the media, Prof Ian Wilmut spoke in front of the US Congress and the House of Commons Science and Technology Committee as part of their enquiries into cloning.
Therapeutic cloning, where cloned human embryos are created for the sole purpose of producing embryonic stem cells for clinical research or use, is permitted by law in the UK but is very tightly controlled by the government. In therapeutic cloning, the embryos are only ever grown in the lab and aren’t transferred into a surrogate womb. Stem cells produced by therapeutic cloning are a genetic match to their DNA donor, who could be a patient with a disease such as motor neuron disease or diabetes. Stem cells which have been cloned from patients like these can be studied by scientists to discover more about what happens to cells in these diseases or could provide a source of patient-matched stem cells to replace faulty cells in the patient’s body.
Although scientists have produced human embryos by therapeutic cloning, iPS cell technology is a more efficient method of producing patient-specific stem cells and has fewer ethical concerns attached to it. As a result, it is now a far more commonly used method than therapeutic cloning. Therapeutic cloning in the UK is regulated by the Human Fertilisation and Embryology Authority.
This short video from EuroStemCell, featuring Professor Sir Ian Wilmut who led the research which produced Dolly, explains the difference between reproductive cloning and therapeutic cloning and discusses the ethical issues associated with them.
At the moment, it seems unlikely that cloning by techniques like SCNT will play a major role in future scientific research unless the success rate is dramatically improved. However, it is impossible to predict what will happen in science – before 1997 most scientists would have claimed that Dolly could never be created.
Quite a few other species have been cloned since Dolly; from mice, rats and rabbits to dogs, cats, monkeys and wolves.