2014考研英語：閱讀理解基礎(chǔ)階段練習題(四)_跨考網(wǎng)

　　2014考研英語：閱讀理解基礎(chǔ)階段練習題(四)

　　Text 4

　　Although the use of cloning to produce copies of humans has been suggested, many people would judge this to be morally wrong. In addition, the prospect of cloning humans raises false expectations, since human personality is only partly determined by genes. Cloning a sick or dying relative would provide a genetically identical copy of that person, but this new individual would likely develop a quite different personality. Similarly, a copy of an athlete, movie star, or scientist might well choose another career because of chance events during his or her lifetime. One hypothetical scenario involves a childless couple who wish to make a copy of one or the other partner rather than having a child by artificial insemination. The social concern is that the parents would not be able to treat naturally a child who was a copy of one of them.

　　The impetus behind the research that led to Dolly was not to find a way to clone humans but rather to develop genetically engineered animals that would serve a variety of purposes. As there are great genetic differences in cattle herds and sheep flocks, breeding copies of selected livestock would increase the efficiency of agricultural productivity and help improve/boost the quality of such commercial products as milk, beef, and wool.

　　As in the management of other breeding schemes, it will be important for scientists to maintain the balance between intense selection of livestock and the maintenance of genetic variability. Preservation of frozen cells from a large number of representatives of different breeds would allow nuclei from those donor cells to be used as required. The ethical issues in animal cloning are perhaps less controversial than with humans; nevertheless, some people worry that producing large number of animal clones only increase the likelihood that these animals will be mistreated.

　　Genetic modification of livestock will also provide new opportunities in medicine and research. Today many patients in need of transplants die before organs become available from suitable donors. Cloning pigs has been suggested as a means of rapidly achieving xenotransplantation, the use of animal organs to replace organs in human patients. Organs transplanted between species are in danger of being destroyed within minutes by the acute immune response of the body receiving the transplant; however, strategies are being developed to modify pigs genetically so that rejection by the immune system may be effectively prevented. (394 words)