【素材】Module 8 Unit 2素材.docx

What is cloning?Cloning means the production of genetically identical animals. In 1995 scientists at the Roslin Institute in Edinburgh, Scotland produced Megan and Morag - two lambs cloned from a single embryo. In 1996 Dolly the sheep was produced, the first example of a clone produced not from an embryo cell but from a cell taken from an adult sheep. She was cloned using a nuclear transfer technique, where the nucleus from a cell taken from the mammary gland of an adult sheep was fused with an unfertilized egg from which the nucleus had been removed. 277 cells were fused in this way, resulting in 29 viable embryos which were implanted into surrogate Blackface ewes. One gave birth to Dolly. Dolly died in 2003 after suffering the signs of premature ageing such as arthritis and a liver complaint.The production of Dolly has sparked a cloning frenzy. 1998 saw the arrival of cows cloned using the same technique that produced Megan and Morag 1. The Roslin institute cloned the first pig in 2000 2. In the US in 2001 a rhesus macaque monkey called Tetra was cloned 3. Also in the US in 2002 a cloned kitten was reported 4 in the same year as the first cloned rabbits in France 5. In 2003 the first cloned mule 6, horse 7 and rat 8 were reported.Animal welfareCloning involves many possibilities for detrimental effects on animals. For example, cloned lambs and calves are frequently abnormally large at birth - some have been twice normal size. One cloning expert admitted in 1992 that many cloned calves are abnormal.9 In Australia, a lamb of five times the mean birth weight for the breed has been recorded. In addition, cloned animals are often found to have malformed internal organs.10 Both of these adverse effects were seen in the first Edinburgh experiments in 1995 that led to Megan and Morag. In addition to death through malformed internal organs, one lamb had to be delivered by caesarean section because it had grown to twice its normal size in the womb, and all but one of the five cloned lambs were at least 20% larger than they should have been.Immediately after birth many cloned lambs have breathing difficulties, are lethargic and often will not suckle. As a consequence, perinatal mortality is high. Miscarriage rates are also high; this is thought to be at least in part because of large offspring syndrome.11Cloning techniques also require a great deal of surgical intervention. Those sheep destined to be egg donors undergo hormone injections, followed by surgery to have the egg cells removed. Following nuclear transfer, it is common for the cloned embryos to be surgically implanted into temporary recipient sheep. Six days later, these temporary foster mothers are simply killed and the embryos removed. The embryos are then placed, again surgically, into the surrogate mother ewes. Some deliveries have been achieved via Caesarean section. So the process is far from simple, and the surgery required can reasonably be expected to inflict residual pain.Attempts to create clones of animals that have been already cloned could also result in increased suffering. In France 1999, a calf which was a clone of a clone died aged eight weeks of rapid depletion of blood cells and severe anaemia. The researchers concluded somatic cloning may be the cause of long-term deleterious effects.12One possible application of cloning, suggested by the Roslin team, is the facilitation of farm animal genetic engineering. If successful, the cloning technique could be used to mass produce farm animals which had been genetically engineered to grow faster, bigger or leaner. Cloning could also be used to mass produce animals genetically engineered to produce pharmaceutical proteins in their milk or blood (gene pharming), or for use in xenotransplantation. However, genetic engineering itself has a very poor track record in terms of animal welfare, and the BUAV is appalled at the idea of combining genetic engineering and cloning techniques.Former Archbishop John Habgood has written of the motives behind cloning experiments:But should science be going down this road at all? What is the point of it? The simple answer is - money. The driving force behind most of the research in this field has come from the agricultural industry. I use the word industry deliberately. Cloning is a means of standardising products, and that is what industry always wants. 13It is clear that cloning may cause a great deal of animal suffering. The so-called benefits, such as the production of genetically identical herds or flocks of animals for intensive farming, may be seen as dubious or even highly unethical. The BUAV therefore believes that the practice of cloning should be stopped immediately.About CloningQuite a few people might take a negative attitude towards cloning. They argue that cloning will arouse a lot of moral and ethical problems and that some people would use the technique to develop crime (How will you feel to face a younger but identical twin of you yourself?). All that they worry about are true. But as every coin has two sides, cloning is no exception. Even the father of the worlds first clone Dolly is not for cloning. But he simply goes against cloning people. But what is clone anyway? Up to now Dolly is the only clone in the world. She was created not out of the natural way the union of a sperm and an egg that we are familiar with, but out of the genetic material from an udder cell of a six-year-old sheep. The embryologist Wilmut fused the udder cell with an egg from another sheep, after first removing all genetic material from the egg. The udder cells genes took up residence in the egg and directed it to grow and develop and an identical twin of the original sheep, Dolly was resulted. And that is how a clone is born. As cloning is no longer a science fiction, and with the birth of Dolly, the whole world begins to focus on these high technology and that generate a severe argument mentioned at the beginning of the article. Is it that frightening when speaking of cloning? The answer is yes.Im not denying that clone has certain disadvantages. Actually clone is a double-edge sword, we have to admit. But we can make the best of its bright side. Will you admire the roses beauty as you used to when you discover its thorn? We all know that it is just because the rapid development of economy that has led to the polluted environment and therefore brings a lot of diseases and many an animals dying out. Can we just stop modernizing because of this? The answers are certainly no. Such is the case as cloning. We can gain a lot from it if used properly. We can clone organs patients need badly to help reduce their pain and even save their lives because they are the perfect match. We can also make an extinct creation back to live when necessary. The list goes on and on.There are never going be sufficient reasons that we should stop doing research on the field of cloning. Instead, the future of cloning is prosperous. Since the harm can not be avoided, at least we can try to put it to the least. But it turns out to be the governments duty. In addition, the clone technique has not grown mature yet. What troubles us now is really how to make the program a successful one. Take a second thought, and you might be for cloning too. Questions about Cloning1. Why clone?Research advances over the past decade which have told us that, with a little work, we humans can clone just about anything we want, from frogs to monkeys and probably even ourselves! So, we can clone things, but why would we want to? Lets look at some of the reasons people give to justify cloning. A. Cloning for medical purposesOf all the reasons, cloning for medical purposes has the most potential to benefit large numbers of people. How might cloning be used in medicine? a. Cloning animal models of diseaseMuch of what researchers learn about human disease comes from studying animal models such as mice. Often, animal models are genetically engineered to carry disease-causing mutations in their genes. Creating these transgenic animals is a time-intensive process that requires trial-and-error and several generations of breeding. Cloning technologies might reduce the time needed to make a transgenic animal model, and the result would be a population of genetically identical animals for study.b. Cloning stem cells for researchStem cells are the bodys building blocks, responsible for developing, maintaining and repairing the body throughout life. As a result, they might be used to repair damaged or diseased organs and tissues. Researchers are currently looking toward cloning as a way to create genetically defined human stem cells for research and medical purposes. c. “Pharming” for drug productionFarm animals such as cows, sheep and goats are currently being genetically engineered to produce drugs or proteins that are useful in medicine. Just like creating animal models of disease, cloning might be a faster way to produce large herds of genetically engineered animals.B. Reviving endangered or extinct speciesHave you seen Jurassic Park? In this feature film, scientists use DNA preserved for tens of millions of years to clone dinosaurs. They find trouble, however, when they realize that the cloned creatures are smarter and fiercer than expected. Could we really clone dinosaurs? In theory? Yes. What would you need to do this? A well-preserved source of DNA from the extinct dinosaur and a closely related species, currently living, that could serve as a surrogate mother. In reality? Probably not. Its not likely that dinosaur DNA could survive undamaged for such a long time. However, scientists have tried to clone species that became extinct more recently, using DNA from well-preserved tissue samples. C. Reproducing a deceased petNo joke! If you really wanted to, and if you had enough money, you could clone your beloved family cat. At least one biotechnology company in the United States offers cat cloning services for the privileged and bereaved, and they are now working to clone dogs. But dont assume that your cloned kitty will be exactly the same as the one you know and love.The main reason to clone plants or animals is to mass produce organisms with desired qualities, such as a prize-winning orchid or a genetically engineered animal for instance, sheep have been engineered to produce human insulin. If you had to rely on sexual reproduction (breeding) alone to mass produce these animals, and then you would run the risk of breeding out the desired traits because sexual reproduction reshuffles the genetic deck of cards. Other reasons for cloning might include replacing lost or deceased family pets and repopulating endangered or even extinct species. Whatever the reasons, the new cloning technologies have sparked many ethical debates among scientists, politicians and the general public. Several governments have considered or enacted legislation to slow down, limit or ban cloning experiments outright. It is clear that cloning will be a part of our lives in the future, but the course of this technology has yet to be determined.2. How are clones created? The most common process takes DNA from one cell and puts in a hollowed-out egg. Chemicals and electricity are then used to encourage the new DNA to fuse with the egg and develop into an embryo. This technique is called nuclear transfer.3. Are clones normal, healthy animals?Dolly is, but scientists do not yet know whether this is the exception or the rule. Some early evidence suggests that clones may have health problems and that they may age prematurely.4. Could a human clone be born soon?In theory, yes. The techniques used to create Dolly could be applied to humans. But the technology of reproductive cloning is still in its very early stages and there is much that scientists do not understand. It took more than 200 attempts to make Dolly. The other embryos failed to implant in the surrogate mother or were miscarried. Even if a clone makes it to birth, at present it has a very low chance of surviving into adult life.5. Has anyone said they will make live human clones?A number of people have, including Chicago physicist Dr Richard Seed. However, few experts believe that these people have the skills to succeed.6. Are there any benefits from cloning?Yes. The techniques used have already demonstrated benefits. Polly, another sheep clone at the Roslin Institute in Edinburgh has had a human gene inserted so that it produces a blood clotting agent needed by haemophiliacs in its milk. Cloning of human cells in a laboratory could offer perfectly-matched tissue for surgical or genetic repair of humans. 7. Where does the law stand on live human clones?In the UK, human cloning is already banned(禁止) by law. President Bill Clinton has proposed banning research into producing human clones in the US for five years. Some measures have also been made to establish international agreements banning live human clones.8. What animals have been cloned? Scientists have been cloning animals for many years. In 1952, the first animal, a tadpole, was cloned. Before the creation of Dolly, the first mammal cloned from the cell of an adult animal, clones were created from embryonic cells. Since Dolly, researchers have cloned a number of large and small animals including sheep, goats, cows, mice, pigs, cats, rabbits, and a gaur. All these clones were created using nuclear transfer technology. Hundreds of cloned animals exist today, but the number of different species is limited. Attempts at cloning certain species such as monkeys, chickens, horses, and dogs, have been unsuccessful. Some species may be more resistant to somatic cell nuclear transfer than others. The process of stripping the nucleus from an egg cell and replacing it with the nucleus of a donor cell is a traumatic one, and improvements in cloning technologies may be needed before many species can be cloned successfully. 9. Can organs be cloned for use in transplants? Scientists hope that one day therapeutic cloning can be used to generate tissues and organs for trans-plants. To do this, DNA would be extracted from the person in need of a transplant and inserted into an enucleated egg. After the egg containing the patients DNA starts to divide, embryonic stem cells that can be transformed into any type of tissue would be harvested. The stem cells would be used to generate an organ or tissue that is a genetic match to the recipient. In theory, the cloned organ could then be transplanted into the patient without the risk of tissue rejection. If organs could be generated from cloned human embryos, the need for organ donation could be significantly reduced. Many challenges must be overcome before “cloned organ” transplants become reality. More effective technologies for creating human embryos, harvesting stem cells, and producing organs from stem cells would have to be developed. The scientists then harvested fetal tissue from the clones and transplanted it into the donor cow. In the three months of observation following the transplant, no sign of immune rejection was observed in the transplant recipient. More research is needed to study the transplantation of organs from “knock-out” pigs o other animals. 10. What are the risks of cloning? Reproductive cloning is expensive and highly inefficient. More than 90% of cloning attempts fail to produce viable offspring. More than 100 nuclear transfer procedures could be required to produce one viable clone. In addition to low success rates, cloned animals tend to have more compromised immune function and higher rates of infection, tumor growth, and other disorders. Japanese studies have shown that cloned mice live in poor health and die early. About a third of the cloned calves born alive have died young, and many of them were abnormally large. Many cloned animals have not lived long enough to generate good data about how clones age. Appearing healthy at a young age unfortunately is not a good indicator of long term survival. Clones have been known to die mysteriously. For example, Australias first cloned sheep appeared healthy and energetic on the day she died, and the results from her autopsy failed to determine a cause of death. Problems also may result from programming errors in the genetic material from a donor cell.11. Should humans be cloned? This is a serious topic. I read a report (Reuters, United Nations, October 8, 2004) about the human cloning. A group of scientists, doctors and legal experts asked the United Nations on Wednesday to seek an advisory opinion from the World Court declaring human cloning to be a “crime against humanity.” Physicians from the American Medical Association and scientists with the American Association for the Advancement of Science have issued formal public statements advising against human reproductive cloning. Currently, the U.S. Congress is considering the passage of legislation that could ban human cloning. In China, the Chinese Government has officially banned research on human cloning for procreation purposes, but allowed remedial cloning. 12. What benef