How do cloning work

There are unanswered questions about the long-term health of clones. In , Dolly died young after developing a lung disease. Conversely, a follow-up study by Kevin Sinclair , a professor of biology at Nottingham University, found cloned animals are capable of ageing healthily. His study of four seven-year-old Finn-Dorset sheep clones — called, Debbie, Denise, Dianna and Daisy — showed each of the animals had aged healthily and outlived Dolly.

The University of Nottingham academic said in the coming months the sheep will be euthanised and the most detailed study of large cloned animals will be undertaken. Although there are limited tests of human stem cell cloning being carried out, Brody says the most likely application of cloning in coming years will remain in animals. Sinclair believes "one of the main applications" of cloning in the future will be creating transgenic animals and adding them to the food production chain.

Transgenic animals are those that have had a gene inserted into their genome. This process has the potential to eradicate disease by rewriting genes related to diseases. But this also comes with its own ethical issues and in Europe, for example, there is a ban on introducing cloned animal products to the food chain. Elsewhere, Italian researcher Pasqualino Loi and his colleagues have been working on a method that combines gene reprogramming with SCNT cloning techniques.

There are other medical and scientific reasons for the interest in cloning. It is already being used alongside genetic techniques in the development of animal organs for transplant into humans xenotransplantation.

Combining such genetic techniques with cloning of pigs achieved for the first time in March would lead to a reliable supply of suitable donor organs. However, there are still worries about virus transmission. The study of animal clones and cloned cells could lead to greater understanding of the development of the embryo and of ageing and age-related diseases.

Cloned mice become obese, with related symptoms such as raised plasma insulin and leptin levels, though their offspring do not and are normal. Cloning could be used to create better animal models of diseases, which could in turn lead to further progress in understanding and treating those diseases.

It could even enhance biodiversity by ensuring the continuation of rare breeds and endangered species. Dolly, probably the most famous sheep in the world, lived a pampered existence at the Roslin Institute. She mated and produced normal offspring in the normal way, showing that such cloned animals can reproduce.

Born on 5 July , she was euthanased on 14 February , aged six and a half. Sheep can live to age 11 or 12, but Dolly suffered from arthritis in a hind leg joint and from sheep pulmonary adenomatosis, a virus-induced lung tumour to which sheep raised indoors are prone. On 2 February , Australia's first cloned sheep died unexpectedly at the age of two years and 10 months. The cause of death was unknown and the carcass was quickly cremated as it was decomposing.

However, her early ageing may reflect that she was raised from the nucleus of a 6-year old sheep. Study of her cells also revealed that the very small amount of DNA outside the nucleus, in the mitochondria of the cells, is all inherited from the donor egg cell, not from the donor nucleus like the rest of her DNA.

So she is not a completely identical copy. This finding could be important for sex-linked diseases such as haemophilia, and certain neuromuscular, brain and kidney conditions that are passed on through the mother's side of the family only. Scientists are working on ways to improve the technology. For example, when two genetically identical cloned mice embryos are combined, the aggregate embryo is more likely to survive to birth.

Improvements in the culture medium may also help. Most of the ethical concerns about cloning relate to the possibility that it might be used to clone humans. There would be enormous technical difficulties. As the technology stands at present, it would have to involve women willing to donate perhaps hundreds of eggs, surrogate pregnancies with high rates of miscarriage and stillbirth, and the possibility of premature ageing and high cancer rates for any children so produced.

However, in South Korean scientists announced that they had cloned 30 human embryos, grown them in the laboratory until they were a hollow ball of cells, and produced a line of stem cells from them. The FDA action means that researchers are now free to using cloning methods to make copies of animals with desirable agricultural traits, such as high milk production or lean meat.

However, because cloning is still very expensive, it will likely take many years until food products from cloned animals actually appear in supermarkets. Another application is to create clones to build populations of endangered, or possibly even extinct, species of animals.

In , researchers produced the first clone of an endangered species: a type of Asian ox known as a guar. Sadly, the baby guar, which had developed inside a surrogate cow mother, died just a few days after its birth. In , another endangered type of ox, called the Banteg, was successfully cloned. Soon after, three African wildcats were cloned using frozen embryos as a source of DNA.

Although some experts think cloning can save many species that would otherwise disappear, others argue that cloning produces a population of genetically identical individuals that lack the genetic variability necessary for species survival. Some people also have expressed interest in having their deceased pets cloned in the hope of getting a similar animal to replace the dead one. But as shown by Cc the cloned cat, a clone may not turn out exactly like the original pet whose DNA was used to make the clone.

Reproductive cloning is a very inefficient technique and most cloned animal embryos cannot develop into healthy individuals. For instance, Dolly was the only clone to be born live out of a total of cloned embryos. This very low efficiency, combined with safety concerns, presents a serious obstacle to the application of reproductive cloning.

Researchers have observed some adverse health effects in sheep and other mammals that have been cloned. These include an increase in birth size and a variety of defects in vital organs, such as the liver, brain and heart. Other consequences include premature aging and problems with the immune system. Another potential problem centers on the relative age of the cloned cell's chromosomes. As cells go through their normal rounds of division, the tips of the chromosomes, called telomeres, shrink.

Over time, the telomeres become so short that the cell can no longer divide and, consequently, the cell dies. This is part of the natural aging process that seems to happen in all cell types. As a consequence, clones created from a cell taken from an adult might have chromosomes that are already shorter than normal, which may condemn the clones' cells to a shorter life span. Indeed, Dolly, who was cloned from the cell of a 6-year-old sheep, had chromosomes that were shorter than those of other sheep her age.

Dolly died when she was six years old, about half the average sheep's year lifespan. Therapeutic cloning involves creating a cloned embryo for the sole purpose of producing embryonic stem cells with the same DNA as the donor cell. These stem cells can be used in experiments aimed at understanding disease and developing new treatments for disease.

To date, there is no evidence that human embryos have been produced for therapeutic cloning. The richest source of embryonic stem cells is tissue formed during the first five days after the egg has started to divide.

At this stage of development, called the blastocyst, the embryo consists of a cluster of about cells that can become any cell type. Stem cells are harvested from cloned embryos at this stage of development, resulting in destruction of the embryo while it is still in the test tube.

Researchers hope to use embryonic stem cells, which have the unique ability to generate virtually all types of cells in an organism, to grow healthy tissues in the laboratory that can be used replace injured or diseased tissues.

In addition, it may be possible to learn more about the molecular causes of disease by studying embryonic stem cell lines from cloned embryos derived from the cells of animals or humans with different diseases. Finally, differentiated tissues derived from ES cells are excellent tools to test new therapeutic drugs.

Many researchers think it is worthwhile to explore the use of embryonic stem cells as a path for treating human diseases. However, some experts are concerned about the striking similarities between stem cells and cancer cells.

Both cell types have the ability to proliferate indefinitely and some studies show that after 60 cycles of cell division, stem cells can accumulate mutations that could lead to cancer. Therefore, the relationship between stem cells and cancer cells needs to be more clearly understood if stem cells are to be used to treat human disease. Gene cloning is a carefully regulated technique that is largely accepted today and used routinely in many labs worldwide.

However, both reproductive and therapeutic cloning raise important ethical issues, especially as related to the potential use of these techniques in humans. Reproductive cloning would present the potential of creating a human that is genetically identical to another person who has previously existed or who still exists. This may conflict with long-standing religious and societal values about human dignity, possibly infringing upon principles of individual freedom, identity and autonomy.