2020英语专四阅读练习100篇附答案:生物知识

2020-08-27 07:29:00来源:网络

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 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. overthe past ten years. But genetic engineering of treeshas lagged 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 isa 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 andsequencing the estimated 100,00 genes in human cells. similar efforts to analyzetree genesare still 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 alsogaining ground. To this end, Dr.Amerson and his colleagues are taking part in the Pine GeneDiscovery Project. an initiative to identify and sequence the 50,000-odd genes in the pinetree's genome. Knowing which gene does what should make it easier to know what to alter.

  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.

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