Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Thinking Tool Data grid What are the issues related to cloning? Questions What is cloning? Sources Drell, Daniel, and Marissa Mills. "Cloning Fact Sheet." Oak Ridge National Laboratory. 30 July 2008. 25 Sep. 2009 <http://www.ornl.gov/sci/techresou rces/Human_Genome/elsi/cloning.s html>. How/Why is cloning performed? One of the biggest disadvantages of cloning is that the technology is still so uncertain. Dolly the sheep, the first mammalian clone, was born in 1996. While she was initially successful, she died young of a disease not normally seen in sheep of her age. Scientists are still unsure of any genetic mutations that might occur when an animal is cloned. Also, while Dolly was a successful clone, there were hundreds of failed clones before she was made, including several dead fetuses. Other cloned animals have turned out horribly deformed. Losing gene diversity is another of the disadvantages of cloning. When the media report on cloning in the news, they are usually talking about only one type called reproductive cloning. There are different types of cloning however, and cloning technologies can be used for other purposes besides producing the genetic twin of another organism. To "clone a gene," a DNA fragment containing the gene of interest is isolated from chromosomal DNA using restriction enzymes and then united with a plasmid that has been cut with the same restriction enzymes. When the fragment of chromosomal DNA is joined with its cloning vector in the lab, it is called a "recombinant DNA molecule." Following introduction into suitable host cells, the recombinant DNA can then be reproduced along with the host cell DNA. "What is Cloning?." Learn Genetics. 15 Sep. 2009 <learn.genetics.utah.edu/content/te ch/cloning/whatiscloning/> What exactly is cloning? Cloning is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two! You might not believe it, but there are human clones among us right now. They weren't made in a lab, though: they're identical twins, created naturally. Below, we'll see how natural identical twins relate to modern cloning technologies. What are the side effects? 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 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. Should humans be cloned? 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. The U.S. Congress has considered the passage of legislation that could ban human cloning. Due to the inefficiency of animal cloning (only about 1 or 2 viable offspring for every 100 experiments) and the lack of understanding about reproductive cloning, many scientists and physicians strongly believe that it would be unethical to attempt to clone humans. Not only do most attempts to clone mammals fail, about 30% of clones born alive are affected with "large-offspring syndrome" and other debilitating conditions. Several cloned animals have died prematurely from infections and other complications. The same problems would be expected in human cloning. In addition, scientists do not know how cloning could impact mental development. While factors such as intellect and mood may not be as important for a cow or a mouse, they are crucial for the development of healthy humans. With so many unknowns concerning reproductive cloning, the attempt to clone humans at this time is considered potentially dangerous and ethically irresponsible. 1. High failure rate Research advances over the past decade 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? Let's look at some of the reasons people give to justify cloning. 1. Cloning for medical purposes Of all the reasons, cloning for medical purposes has the most potential to benefit large numbers of people. How might cloning be used in medicine? Cloning animal models of disease Much 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 Cloning animals through somatic cell nuclear transfer is simply inefficient. The success rate ranges from 0.1 percent to 3 percent, which means that for every 1000 tries, only one to 30 clones are made. Or you can look at it as 970 to 999 failures in 1000 tries. That's a lot of effort with only a speck of a return! 2. Problems during later development Cloned animals that do survive tend to be much bigger at birth than their natural counterparts. Scientists call this "Large Offspring Syndrome" (LOS). Clones with LOS have abnormally large organs. This can lead to breathing, blood flow and other problems. Because LOS doesn't always occur, scientists cannot reliably predict whether it will happen in any given clone. Also, some clones without LOS have developed kidney or brain malformations and impaired immune systems, which can cause problems later in life. The prospect of cloning humans is highly controversial and raises a number of ethical, legal and social challenges that need to be considered. To explore some of these, see What are Some Issues in Cloning? Why would anyone want to clone humans? Some reasons include: ♥ To help infertile couples have children ♥ To replace a deceased child From a technical standpoint, before humans are cloned, we need to have a good idea of the risks involved. How sure can we be that a cloned baby will be healthy? What might go wrong? Thinking Tool Data grid a population of genetically identical animals for study. 3. Abnormal gene expression patterns Cloning stem cells for research Stem cells are the body's 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. To see how this is done, see Creating Stem Cells for Research, a component of the Stem Cells in the Spotlight module. "Pharming" for drug production Farm 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. Find out more about this research in the feature articlePharming for Farmaceuticals . 2. Reviving Endangered or Extinct Species Have 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. It's 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. In cloning, the transferred nucleus doesn't have the same program as a natural embryo. It is up to the scientist to reprogram the nucleus, like teaching an old dog new tricks. Complete reprogramming is needed for normal or near-normal development. Incomplete programming will cause the embryo to develop abnormally or fail. 4. Telomeric differences When scientists looked at the telomere lengths of cloned animals, they found no clear answers. Chromosomes from cloned cattle or mice had longer telomeres than normal. These cells showed other signs of youth and seemed to have an extended lifespan compared with cells from a naturally conceived cow. On the other hand, Dolly the sheep's chromosomes had shorter telomere lengths than normal. This means that Dolly's cells were aging faster than the cells from a normal sheep. Thinking Tool Data grid "Cloning-Article."GoldBamboo.com Your Integrative Health and Wellness Resource. 22 July 2006. 16 Sep. 2009 <http://www.goldbamboo.com/topi c-t2730-a1-6Cloning.html>. "Cloning." Free Website Hosting – Angelfire free website templates to make your own free website. 14 Sep. 2009 <http://www.angelfire.com/la/Isla micView/Cloning.html>. Cloning is the process of creating an identical copy of an original. A clone in the biological sense, therefore, is a single cell (like bacteria, lymphocytes etc.) or multi-cellular organism that has been directly copied from and is therefore genetically identical to another living organism. Sometimes this term can refer to "natural" clones made either when an organism reproduces asexually or when two genetically identical individuals are produced by chance (as with identical twins), but in common parlance, a clone is an identical copy created intentionally. (See also: clone (genetics). The success rate of cloning has been low: Dolly the sheep was born after 277 eggs were to create 29 embryos, which only produced three lambs at birth, only one of which lived, Dolly. 70 calves have been created from 9,000 attempts and one third of them died young; Prometea took 328 attempts, and, more recently, Paris Texas was created after 400 attempts. Notably, although the first clones were frogs, no adult cloned frog has yet been produced from a somatic adult nucleus donor cell. Cloning is quite inefficient and usually there are over 600 to 1000 nuclear transfers before one is able to grow into a stem cell. This inefficiency is thought to be due to geneticimprinting in the cloned adult cell that interferes with the correct gene expression in the embryo. Even those animals that are successfully cloned are not as healthy as the original animal. For example, Dolly had arthritis and sign of premature aging. See methylation and epigenetic. Cloning is done by the use of the nucleus of an egg and selected DNA from the one being cloned. These two are than fused together with the use of an electrical current. This cell than grows into a genetic duplicate and placed into the womb until full term into a normal human being. At least this is the theory. So a clone is not an identical person to the one being cloned in all respects. Just as an identical twin is not the twin in all respects. They are two distinct human beings, if one dies the other lives on. Cloning should not be mistaken with the ability to live forever. It is just a genetic duplicate, the two would look the same, have some of the same likes and dislikes but would be two separate distinct human beings. SUMMARY Human cloning Main article: Human cloning Human cloning is the creation of a genetically identical copy of an existing, or previously existing human or growing cloned tissue from that individual. The term is generally used to refer to artificial human cloning; human clones in the form of identical twins are commonplace, with their cloning occurring during the natural process of reproduction. Thinking Tool Data grid