點擊查看：2018年6月大學(xué)英語六級閱讀100篇

　　If you go down to the woods today, you may meet high-tech trees genetically modified to speed their growthor improve the quality of their wood. Genetically-engineered food crops have become increasingly common, albeit controversial. over the past ten years. But genetic engineering of trees has lagged behind.

　　Part of the reason is technical. Understanding. and then altering, the genes of a big pine tree are more complex than creating a better tomato. While tomatoes sprout happily, and rapidly, in the laboratory, growing a whole tree from a single, genetically altered cell in a test tube is a tricky process that takes years, not months. Moreover. little is known about tree genes. Some trees, such as pine trees. have a lot of DNA-roughly ten times as much as human. And, whereas the Human Genome Project is more than half-way throughits task of isolating and sequencing the estimated 100,00 genes in human cells. similar efforts to analyzetree genes are still just saplings (幼苗).

　　Given the large number of tree genes and the little that is known about them, tree engineers are starting with a search for genetic "markers". The first step is to isolate DNA from trees with desirable propertiessuch as insect resistance. The next step is to find stretches of DNA that show the presence of a particular gene. Then, when you mate two trees with different desirable properties, it is simple to check which offspring contain them all by looking for the genetic markers. Henry Amerson, at North Carolina State University, is using genetic markers to breed fungal resistance into southern pines. Billions of these are grown across America for pulp and paper, and outbreaks of disease are expensive. But not all individual trees are susceptible. Dr. Amerson’s group has found markers that distinguish fungus-resistant stock from disease-prone trees.Using traditional breeding techniques, they are introducing the resistance genes into pines on test sites in America.

　　Using generic markers speeds up old-fashioned breeding methods becauseyou no longer have to wait for the tree to grow up to see if it has the desiredtraits. But it is more a sophisticated form of selective breeding. Now. however.interest in genetic tinkering (基因修補) is also gaining ground. To this end, Dr.Amerson and his colleagues are taking part in the Pine Gene Discovery Project. an initiative to identify and sequence the 50,000-odd genes in the pine tree's genome. Knowing which gene does what should make it easier to know what to alter.

　　1. Compared with genetic engineering of food crops, genetic engineering of trees____________________.

　　A) began much later

　　B) has developed more slowly

　　C) is less useful

　　D) was less controversial

　　2. What does the author think about the genetic engineering of pine trees?

　　A) Time-consuming.

　　B) Worthwhile.

　　C) Significant.

　　D) Technically impossible.

　　3. What can we learn about the research on tree genes?

　　A) The research methods are the same as the analysis of human genes.

　　B) The findings are expected to be as fruitful as the analysis of human genes.

　　C) It will take as much time and effort as the analyst, of human genes.

　　D) The research has been mainly concentrated on the genes of young trees.

　　4. It is discovered by Henry Amerson’s team that_______________.

　　A) southern pines cannot resist fungus

　　B) all southern pines are not susceptible

　　C) the genetic marker in southern pines was the easiest to identify

　　D) fungus-resistant genes came originally from outside the U.S.A.

　　5. What is the primary objective of carrying out the Pine Gene Discovery Project?

　　A) To speed up old-Fashioned breeding methods.

　　B) To identify all the genes in the pine tree's genome.

　　C) To find out what desired traits the pine trees have.

　　D) To make it easier to know which gene needs altering.

　　答案：

　　1.相較于糧食作物的基因工程，樹木的基因工程______________。

　　A)開始得較晚

　　B)發(fā)展得較慢

　　C)用處較小

　　D)爭議性較低

　　[B]本文并沒有提到樹木基因改良技術(shù)從什么時候開始，所以有可能樹木的基因改良技術(shù)和別的基因改良技術(shù)在開始的時間上相差不大，但在所取得的成果方面卻有很大的差別，因此，本題關(guān)鍵在于理解首段末句中的lag behind指的是程度上的落后，而非時間上的落后，故B正確。

　　2.作者對于松樹基因工程怎么看?

　　A)耗時。

　　B)十分值得。

　　C)很重要。

　　D)技術(shù)上不可能。

　　[B]第2段第3句中的that takes years表明研究樹木的基因改造技術(shù)將花費很長時間，因此選項A為本題答案。原文沒有就選項B和C兩方面做出討論，因此不能推斷出這兩個選項;雖然第2段首句提到technical一詞，但文章表明樹木基因改造技術(shù)是可行的。只是會花費較多的時問，因此選項D也不正確。

　　3.對于樹木基因進行的研究，我們了解到什么?

　　A)研究方法與分析人類基因時相同。

　　B)人們預(yù)計研究成果會與人類基因分析一樣碩果累累。

　　C)所花的時間和精力與人類基因分析一樣多。

　　D)研究主要關(guān)注在小樹的基因上面。

　　[A]第2段末句中的similar cfforts指的就是task of isolating and sequencing，即分析基因的常用方法。該句表明人類基因和樹種基因的分析方法相同，但進展有差別，因此選項A為正確的推斷。

　　4.Henry Amerson的研究小組發(fā)現(xiàn)，__________________。

　　A)南部黃松不能抵抗真菌

　　B)并不是所有的南部黃松都很容易染病

　　C)南部黃松的基因標(biāo)記最容易識別

　　D)有真菌抵抗能力基因源自國外而非美國

　　[B]選項B是一個半否定的句式，因此本題關(guān)鍵在于理解選項B的Al1...are not...結(jié)構(gòu)在意義上等同于第3段倒數(shù)第3句的not all... are...。第3段倒數(shù)第2句中的fungus-resistant stock指的是南方松樹中能抗真菌的樹種，并非別的與南方松樹毫不相關(guān)的樹種，因此A的說法不正確。

　　5.開展“松樹基因發(fā)現(xiàn)項目”的主要目的是什么?

　　A)加快舊式的育種方法。

　　B)識別松樹基因組中的所有基因。

　　C)找到松樹所具有的優(yōu)質(zhì)特點。

　　D)讓發(fā)現(xiàn)什么基因需要做改變的過程變得更加簡單。

　　[B]末段倒數(shù)第2句中的an initiative...是the Pine Gene Discovery Project的同位語，表明開展該計劃的目的，因此選項B為本題答案。其他選項都是在完成該計劃后能夠達成的工作，它們都要以松樹基因的排列組合為基礎(chǔ)，因此，這些選項都不是primary objective，而是在實現(xiàn)了primary objective之后繼續(xù)進行的工作。

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