考研英语阅读真题文章三十篇之十三
<p> <span word="From">From</span> <span word="Genes">Genes</span> <span word="to">to</span> <span word="GMOs">GMOs</span></p><p> <span word="Today">Today</span>, <span word="genes">genes</span> <span word="can">can</span> <span word="be">be</span> <span word="isolated">isolated</span>, <span word="identified">identified</span>, <span word="and">and</span> <span word="cloned">cloned</span>, <span word="then">then</span> <span word="inserted">inserted</span> <span word="into">into</span> <span word="other">other</span> <span word="organisms">organisms</span> <span word="to">to</span> <span word="alter">alter</span> <span word="their">their</span> <span word="traits">traits</span>. <span word="The">The</span> <span word="process">process</span> <span word="is">is</span> <span word="called">called</span> <span word="genetic">genetic</span> <span word="engineering">engineering</span>. <span word="For">For</span> <span word="this">this</span> <span word="technology">technology</span> <span word="to">to</span> <span word="develop">develop</span>, <span word="a">a</span> <span word="few">few</span> <span word="tools">tools</span> <span word="were">were</span> <span word="necessary">necessary</span>. <span word="In">In</span> <span word="the">the</span> 1970<span word="s">s</span>, <span word="scientists">scientists</span> <span word="isolated">isolated</span> <span word="bacterial">bacterial</span> <span word="plasmids">plasmids</span>. <span word="These">These</span> <span word="are">are</span> <span word="hula">hula</span> <span word="hoop">hoop</span> <span word="shaped">shaped</span> <span word="double">double</span> <span word="stranded">stranded</span> <span word="units">units</span> <span word="of">of</span> <span word="DNA">DNA</span> <span word="that">that</span> <span word="can">can</span> <span word="be">be</span> <span word="moved">moved</span> <span word="easily">easily</span> <span word="from">from</span> <span word="one">one</span> <span word="cell">cell</span> <span word="to">to</span> <span word="another">another</span>. <span word="They">They</span> <span word="also">also</span> <span word="discovered">discovered</span> <span word="scissors">scissors</span>, <span word="called">called</span> <span word="restriction">restriction</span> <span word="enzymes">enzymes</span> <span word="for">for</span> <span word="cutting">cutting</span> <span word="the">the</span> <span word="DNA">DNA</span> <span word="into">into</span> <span word="predictable">predictable</span>, <span word="reproducible">reproducible</span> <span word="patterns">patterns</span>. <span word="These">These</span> <span word="enzymes">enzymes</span> <span word="are">are</span> <span word="used">used</span> <span word="to">to</span> <span word="snip">snip</span> <span word="apart">apart</span> <span word="plasmids">plasmids</span> <span word="at">at</span> <span word="very">very</span> <span word="specific">specific</span> <span word="DNA">DNA</span> <span word="sequences">sequences</span>, <span word="leaving">leaving</span> <span word="free">free</span> <span word="ends">ends</span> <span word="that">that</span> <span word="can">can</span> <span word="be">be</span> <span word="rejoined">rejoined</span> <span word="as">as</span> <span word="the">the</span> <span word="scientist">scientist</span> <span word="chooses">chooses</span>. <span word="Restriction">Restriction</span> <span word="enzymes">enzymes</span> <span word="occur">occur</span> <span word="in">in</span> <span word="bacteria">bacteria</span> <span word="as">as</span> <span word="part">part</span> <span word="of">of</span> <span word="a">a</span> <span word="natural">natural</span> <span word="defense">defense</span> <span word="mechanism">mechanism</span> <span word="to">to</span> <span word="guard">guard</span> <span word="against">against</span> <span word="invading">invading</span> <span word="viruses">viruses</span>. <span word="Many">Many</span> <span word="different">different</span> <span word="types">types</span> <span word="are">are</span> <span word="now">now</span> <span word="available">available</span>, <span word="each">each</span> <span word="cutting">cutting</span> <span word="DNA">DNA</span> <span word="at">at</span> <span word="a">a</span> <span word="different">different</span> <span word="sequence">sequence</span> <span word="of">of</span> <span word="base">base</span> <span word="pairs">pairs</span>.</p><p> <span word="Once">Once</span> <span word="a">a</span> <span word="plasmid">plasmid</span> <span word="is">is</span> <span word="snipped">snipped</span> <span word="open">open</span>, <span word="a">a</span> <span word="foreign">foreign</span> <span word="piece">piece</span> <span word="of">of</span> <span word="DNA">DNA</span>, <span word="cut">cut</span> <span word="by">by</span> <span word="the">the</span> <span word="same">same</span> <span word="enzyme">enzyme</span> <span word="scissors">scissors</span>, <span word="can">can</span> <span word="be">be</span> <span word="taped">taped</span>, <span word="end">end</span> <span word="to">to</span> <span word="end">end</span>, <span word="into">into</span> <span word="the">the</span> <span word="plasmid">plasmid</span> <span word="using">using</span> <span word="another">another</span> <span word="enzyme">enzyme</span>, <span word="DNA">DNA</span> <span word="ligase">ligase</span>. <span word="This">This</span> <span word="is">is</span> <span word="the">the</span> <span word="glue">glue</span> <span word="that">that</span> <span word="sticks">sticks</span> <span word="all">all</span> <span word="the">the</span> <span word="pieces">pieces</span> <span word="together">together</span>. <span word="The">The</span> <span word="new">new</span> <span word="plasmid">plasmid</span> <span word="is">is</span> <span word="inserted">inserted</span> <span word="back">back</span> <span word="into">into</span> <span word="a">a</span> <span word="cell">cell</span>, <span word="where">where</span> <span word="numerous">numerous</span> <span word="copies">copies</span> <span word="can">can</span> <span word="be">be</span> <span word="made">made</span>. <span word="Introduction">Introduction</span> <span word="of">of</span> <span word="specific">specific</span> <span word="genetic">genetic</span> <span word="material">material</span> <span word="into">into</span> <span word="rapidly">rapidly</span> <span word="reproducing">reproducing</span> <span word="target">target</span> <span word="bacteria">bacteria</span> <span word="can">can</span> <span word="turn">turn</span> <span word="the">the</span> <span word="cells">cells</span> <span word="into">into</span> <span word="miniature">miniature</span> <span word="factories">factories</span> <span word="for">for</span> <span word="production">production</span> <span word="of">of</span> <span word="useful">useful</span> <span word="substances">substances</span>. <span word="For">For</span> <span word="example">example</span>, <span word="when">when</span> <span word="the">the</span> <span word="Exxon">Exxon</span> <span word="Valdez">Valdez</span> <span word="oil">oil</span> <span word="freighter">freighter</span> <span word="ran">ran</span> <span word="aground">aground</span> <span word="in">in</span> 1989 <span word="and">and</span> <span word="spilled">spilled</span> <span word="thirty">thirty</span> <span word="eight">eight</span> <span word="million">million</span> <span word="liters">liters</span> <span word="of">of</span> <span word="oil">oil</span>, <span word="oil">oil</span> <span word="eating">eating</span> <span word="bacteria">bacteria</span>, <span word="created">created</span> <span word="in">in</span> <span word="just">just</span> <span word="this">this</span> <span word="manner">manner</span>, <span word="were">were</span> <span word="used">used</span> <span word="in">in</span> <span word="the">the</span> <span word="cleanup">cleanup</span> <span word="operation">operation</span>. <span word="The">The</span> <span word="oil">oil</span> <span word="was">was</span> <span word="broken">broken</span> <span word="down">down</span> <span word="five">five</span> <span word="times">times</span> <span word="faster">faster</span> <span word="with">with</span> <span word="help">help</span> <span word="from">from</span> <span word="the">the</span> <span word="genetically">genetically</span> <span word="modified">modified</span> <span word="organisms">organisms</span> .</p>
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