考研英语历年真题来源报刊阅读100篇 Text99
来源：中国研究生招生网 作者： 时间：2008-08-30 20:51:47
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From Genes to GMOs
Today, genes can be isolated, identified, and cloned, then inserted into other organisms to alter their traits. The process is called genetic engineering. For this technology to develop, a few tools were necessary. In the 1970s, scientists isolated bacterial plasmids. These are hulahoopshaped doublestranded units of DNA that can be moved easily from one cell to another. They also discovered "scissors," called restriction enzymes for cutting the DNA into predictable, reproducible patterns. These enzymes are used to"snip apart" plasmids at very specific DNA sequences, leaving free ends that can be rejoined as the scientist chooses. Restriction enzymes occur in bacteria as part of a natural defense mechanism to guard against invading viruses. Many different types are now available, each cutting DNA at a different sequence of base pairs.
Once a plasmid is snipped open, a foreign piece of DNA, cut by the same enzyme scissors, can be taped, end to end, into the plasmid using another enzyme, DNA ligase. This is the glue that sticks all the pieces together. The new plasmid is inserted back into a cell, where numerous copies can be made. Introduction of specific genetic material into rapidly reproducing target bacteria can turn the cells into miniature factories for production of useful substances. For example, when the Exxon Valdez oil freighter ran aground in 1989 and spilled thirtyeight million liters of oil, oileating bacteria, created in just this manner, were used in the cleanup operation. The oil was broken down five times faster with help from the genetically modified organisms (GMOs).
Plasmid technology has also been developed for moving targeted genetic material into plants. In this technique, scientists use the plasmid from a bacterium that causes tumors on plants. In nature, this bacterium transfers genetic material into plant tissues by releasing plasmids onto damaged plant cells. The plasmids enter the plant tissue and produce a swelling, or tumor. Because of this special ability to invade plant tissue, these tumorinducing (TI) plasmids are now used routinely as "taxi cabs" to carry target genes into a wide variety of plant cells, including, for example, corn. The European corn borer is a common pest in this economically valuable crop. When pesticides are used against them, timing is critical. If sprayed too late, the corn borer will already have made a home inside the corn stem and will not be killed. CIBA Research was the first company to develop what has become commonly known as Bt corn. It contains genes that allow it to resist infestation by the corn borer. The Bt genes came from a bacterium called Bacillus thuring ensis . It produces a protein called Bt protoxin. When an insect larva eats these bacteria, the toxin contained in the bacterium attaches to the insect's gut and makes holes in it, and the larva starves to death. Bt corn can be grown using less pesticide, and sometimes even no pesticide.
v.隔离，孤立
［真题例句］ Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots.［1998年阅读5］
［例句精译］ 地球上散落分布着100多个相互独立的小火山活动区，地质学家称之为热点。
trait
n.特征，特点，特性
［真题例句］ (61) One difficulty is that almost all of what is called behavioral science continues to trace behavior to states of mind, feelings, traits of character, human nature, and so on.［2002年翻译］
［例句精译］ (61)难题之一在于所谓的行为科学几乎全都依然从心态、情感、性格特征、人性等方面去寻找行为的根源。
spill
v.溢出，溅出；n.摔下，跌下
［真题例句］ 54. What the author tries to suggest may best be interpreted as.［1998年阅读1］
［A］ Its no use crying over spilt (v.) milk
［例句精译］ 54作者试图提醒的意思可以最恰当地解释为：。
［A］ "覆水难收"
modify
v.更改，修改，修饰
［真题例句］ In response, schools are modifying their programs, adapting instruction to children who are exceptional, to those who cannot profit substantially from regular programs.［1994年阅读3］
［例句精译］ 作为回应，学校也在调整课程安排，使授课能够适应特殊儿童，适应那些不能从常规课程中真正获益的儿童的需要。
routine
n.例行公事，常规；a.常规的，例行的
［真题例句］ You can make a mental blueprint of a desire as you would make a blueprint of a house, and each of us is continually making these blueprints in the general routine (n.) of everyday living.［1996年阅读1］
［例句精译］ 你可以在头脑里勾画出一幅欲望的蓝图，就像你可以设计房屋的蓝图一样，而我们每个人在日常生活中都在不停地画着这样的蓝图。
［真题例句］ Like other human beings, he encounters moral issues even in everyday performance of his routine (a.) duties-he is not supposed to cook his experiments, manufacture evidence, or doctor his reports. ［2006年翻译］
［例句精译］ 像其他人类一样，普通科学家甚至在每天日常的工作中都遭遇到了道义上的问题--他不应该伪造实验、制造证据或改动他的报告。
infestation
n.(害虫, 盗贼等)群袭, 出没, 横行
