Главная > Реферат >Остальные работы
On February 24, 1997, the scientists at the Roslin Institute in Edinburg, Scotland announced their success in cloning an adult mammal for the first time. The cloned sheep was named Dolly. She was the first animal cloned from a cell taken from an adult. It was an accomplishment than science had declared impossible. In June, 1997, the National Bioethics Advisory Commission issued its recommendation that a ban be placed on all efforts to create a child through cloning or somatic cell nuclear transfer. They urged that the current moratorium on federal funding of human cloning research be continued, and requested private agencies also restrain from such work. At the same time they recommended that this issue be reevaluated after a 3-5 year period of study and reflection.
Dolly was a clone of the sheep (her genetic mother) who provided the udder cell. The package of genes in the nucleus of that udder cell contained exactly the same repertoire of genes as all the rest of her mother’s cells and so Dolly’s genetic makeup was identical to her mother’s. What was novel about Dolly was that she was the first unequivocal mammalian clone. Lower vertebrates had been cloned in the early 1960s when it was shown that a nucleus taken from an adult frog cell transplanted to a frog egg whose own nucleus had been destroyed was able to direct the development of that egg into a swimming tadpole. It was this experiment that first indicated that the genetic content of all our cells, despite the differences between a skin cell and kidney cell, must be more or less the same and retain all the genetic information necessary for an egg to develop into a whole organism.
The cloning of Dolly brought up the possibility of cloning humans. It is illegal in England and Norway. With opinion polls showing overwhelming opposition to cloning human, President Clinton ordered a ban on all federal support for human cloning research and charged the National Bioethics Advisory Commission to report on the ethics of human cloning. This eighteen-member panel of scientists and non scientists concluded that attempting to clone a human being was at this time…morally unacceptable. They recommended continuing the president s ban on the use of federal funds to support cloning of humans, and called federal legislation to prohibit anyone from attempting to create a child through cloning.
California banned human cloning. Meanwhile, the real action was quietly going on in the laboratories, outside the periphery of the public eye. Federally supported experiments in cloning monkeys for use in AIDS vaccine and other research was continuing outside the limelight. What can be done with monkeys can probably be done with people. We are laying the groundwork, one of the scientists said. (Gin Kolata, New York Times)
Dr. Steen Willadsen, one of the scientists who developed techniques used to make Dolly, said it was just a matter of time before the first human is cloned. He is anticipating that cloning will inevitably become an accepted medical procedure, and is now working in a fertility clinic, perfecting techniques that could eventually be used in the cloning of humans.
The complexity of cloning experiments depends on the overall aims of the experiment and the type of source material from which the nucleic acids will be isolated for cloning. Thus a strategy to isolate and sequence a relatively small DNA fragment from E. Coli will be different than a strategy to produce a recombinant protein organism. (An Introduction to Genetic Engineering, Desmond S.T. Nicholl; 6.1) There is no single cloning strategy that will cover all of the cloning requirements.
One way to clone is by cloning from mRNA. This method converts mRNA to DNA (also called copy DNA or cDNA). It uses the enzyme reverse transcriptase to produce complementary DNA. However, there are a few problems with cloning from mRNA. One of them is that the synthesis of full-length cDNAs may be inefficient, particularly if the mRNA is relatively long. More recent methods can overcome this problem. Another method is cloning cDNA in plasmid vectors. Scientists prefer using the bacteriophage vector system, but plasmids are still often used when isolation of the desired cDNA sequence involves screening a small number of clones.
There are also many different methods used in cloning. Three of the main methods used in cloning are blunt-end ligation, linker molecules and homopolymer tailing. Blunt-end ligation is just what it sounds like. The molecules join together using DNA ligase. Linker molecules are self-complementary oligomers that contain a recognition sequence for a particular restriction enzyme. Homoploymer tailing is when enzyme terminal transferase is used to add homopolymers of dA, dT, dG, or dT to a DNA molecule.
Scientists made a number of advances in cloning in 1998. In December, biologists in Japan said they had used a cloning technique to produce eight identical calves from cells removed from an adult cow. In July, researchers at the University of Hawaii announced that they had created more than 50 mice through cloning by using cells from adult mice. An apparent advance on the Roslin technique was reported in August 1997, when scientists at ABS Global Incorporated in DeForest, Wisconsin, a biotechnology company specializing in livestock reproductive services, said that they had produced a calf using a cloning procedure more efficient than that used with Dolly. The Wisconsin scientists began by performing a nuclear transplantation to produce an embryo from a body cell of a 30-day-old bull fetus Then they added another step. They took one of the cells from the embryo they had produced and performed a second nuclear transplantation. The embryo resulting from the second transplantation was then placed in a surrogate mother. The double nuclear transplantation helped make the nucleus even more susceptible to reprogramming and increased the success rate of the procedure. The scientists said that only 15 attempts were required before success was achieved with the birth of the calf, named Gene.
Although ABS Global researchers used a fetus as the source of the nucleus used to produce Gene, they said they were also experimenting with nuclei from the cells of adult cattle. The scientists hoped that their procedure would eventually enable animal breeders to produce an unlimited number of identical animals with superior traits.
If a cell can be taken from a human being and used to create a genetically identical double, then any of us could lose our uniqueness. One would no longer be a self. (George Johnson, Clones and Clones; Pg. 67) Because no cloning technique had been perfected as of mid-1998, scientists expected that any attempt to clone a human would, just as in the work that led to Dolly, result in the death of many embryos and newborns before success was achieved. In addition, even if an infant clone survived, there was no guarantee that it would develop normally. The genetic material in body cells accumulates subtle molecular changes as an organism ages. Because the cell used to create Dolly came from a 6-year-old animal, Dolly s chromosomes had certain characteristics normally found only in older animals. This finding led some scientists to wonder whether Dolly, though appearing normal, might have inherited genetic damage that would eventually show up as premature aging or some other disorder.
I would not be surprised if the cloning of a human will soon be possible, but that is someplace where humans should not be intervening. It is morally wrong to try to create life in a laboratory. God is the only one who should have the control over who has life and who doesn t. When we start playing God and we gain so much control over something as powerful as life itself, it is bound to blow up in our faces. I agree with the National Bioethics Advisory Commision that cloning is at this time morally unacceptable. I hope that we will never become so undiscerning that we make cloning acceptable. Even if someday cloning is morally accepted it will never be morally right.
- On February 27, 1997, it was ... then placed next to each other. Then an electronic ... “President Clinton bans federally funded research on human cloning.” U.S. News. 10 March ... “President Clinton bans federally funded research on human cloning.” U.S. News. 10 March ...
- Cloning Essay, Research Paper Cloning is a shameless act of playing creator. Introduction Cloning is a relevant issue that ... should be created and oppose cloning. In February of 1997, Time and ... what the ruling will be on cloning in the future, it will ...
- Cloning Essay, Research Paper CLONING: HAS SCIENCE GONE TOO FAR? ... patient. Environmentalists have also jumped on the cloning “bandwagon.” There has been ... importance. BIBLIOGRAPHY 1. Bernstein, Maurice M.D. “Cloning of Humans.” February 27, 1997. http://www ...
- Cloning Essay, Research Paper Bioethics, which is ... today is the idea of cloning. On February 23, 1997, Ian Wilmut, ... Joshua Lederberg s 1966 article on cloning in the American Naturalist, ... Voice of America. Britain/Cloning/Ethics. February 25, 1997 http://www ...
- Cloning Essay, Research Paper Cloning Twenty-five years ago, scientists thought that cloning was virtually impossible. In ... To Not Vote On Proposed Cloning Ban.” Washington Bureau. 12 February 1998: 6-7. Robel ...