英语六级阅读理解附详解:生物知识

　　下面是学习啦小编整理的英语六级阅读理解附详解:生物知识，希望对大家有帮助。

　　If you go down to the woods today, you may meethigh-tech trees genetically modified to speed theirgrowthor improve the quality of their wood.Genetically-engineered food crops have becomeincreasingly common, albeit controversial. over thepast ten years. But genetic engineering of trees haslagged behind.

　　Part of the reason is technical. Understanding. and then altering, the genes of a big pine treeare 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 atricky process that takes years, not months. Moreover. little is known about tree genes. Sometrees, 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 andsequencing the estimated 100,00 genes in human cells. similar efforts to analyzetree genes arestill just saplings (幼苗).

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

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

　　如果你今天走到森林里去，可能会看到高科技的树木——这些树通过基因改良促进了生长的速度或提高了木材的质量。基因改造的粮食作物在过去十年里虽然备受争议，却已经越来越普遍，[1]而树木的基因改造工程相对来说还是比较滞后。

　　这其中一个原因是技术问题。了解并改变一棵大松树的基因比制造品质优良的马铃薯复杂多了。马铃薯可在实验室里迅速发芽生长，[2]但要在试管里把经过基因改造的细胞培育成一棵大树却不是几个月就能完成的，要花上好几年的时间呢。而且，对于树木的基因，我们知之甚少。有些树，比如松树，带有大概相当于人类10倍那么岁的DNA。[3]人类染色体工程中分离和排列人类细胞里大概10万个基因的工作已经进展到一半了，而用同样的方法分析树种基因还只是处在萌芽阶段。

　　虽然树木的基因数量巨大，而我们也知之甚少，但是树木基因工程的研究人员正开始寻找基因“标记”。第一步，先把具有优良特性(如具有害虫抵抗性)树种的基因分离出来：下一步，找出带有这个优良基因的DNA片段;接着，让两棵具有不同优良特性的树种杂交，之后通过寻找当中的基因标记就能轻易确定哪棵杂交树苗具有所有特性。北卡罗来纳州立是学的Henry Amerson正运用基因标记技术培育能抵抗真菌的南方松树。这个树种的生长遍布美国，用于制造纸浆和造纸，所以一旦染病，代价昂贵。[4]但是，这种树却不是每一棵都容量染病。Amerson博士的研究小组已经找到区别抗真菌和易染病的树种的基因标记。他们正利用传统的繁殖技术，把这种抗病基因推广到美国的松树试验场。

　　使用基因标记技术，可以加快旧式繁殖的速度，因为你不用等待树苗长大才能看到它是否带有那些你想要的特性。但事实上，这是一种更为复杂的选择性繁殖的技术。不过现在对于基因修补技术的研究也正在升温。[5] 为实现这一目标，Amerson博士和他的同事们正参与一个名为“发现松树基因”的研究工程，其宗旨是为了辨别和排列松树染色体组中的5万余个基因。如果能知道每个基因的功能，就能更容易地知道应该改变哪个基因了。

　　1. Compared with genetic engineering of foodcrops, genetic engineering oftrees____________________.

　　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.