新托福TPO21综合写作训练详细解析：基因改良
<p> 阅读材料：</p><p> <span word="Genetic">Genetic</span> <span word="modification">modification</span>, <span word="a">a</span> <span word="process">process</span> <span word="used">used</span> <span word="to">to</span> <span word="change">change</span> <span word="an">an</span> <span word="organisms">organisms</span> <span word="genes">genes</span> <span word="and">and</span> <span word="hence">hence</span> <span word="its">its</span> <span word="characteristics">characteristics</span>, <span word="is">is</span> <span word="not">not</span> <span word="being">being</span> <span word="used">used</span> <span word="to">to</span> <span word="improve">improve</span> <span word="trees">trees</span>. <span word="Through">Through</span> <span word="genetic">genetic</span> <span word="modification">modification</span>, <span word="it">it</span> <span word="is">is</span> <span word="possible">possible</span> <span word="to">to</span> <span word="create">create</span> <span word="trees">trees</span> <span word="that">that</span> <span word="produce">produce</span> <span word="more">more</span> <span word="fruit">fruit</span>, <span word="grow">grow</span> <span word="faster">faster</span>, <span word="or">or</span> <span word="withstand">withstand</span> <span word="adverse">adverse</span> <span word="conditions">conditions</span>. <span word="Planting">Planting</span> <span word="genetically">genetically</span> <span word="modified">modified</span> <span word="trees">trees</span> <span word="on">on</span> <span word="a">a</span> <span word="large">large</span> <span word="scale">scale</span> <span word="promises">promises</span> <span word="to">to</span> <span word="bring">bring</span> <span word="a">a</span> <span word="number">number</span> <span word="of">of</span> <span word="benefits">benefits</span>.</p><p> 基因改良是通过改变有机体的基因，进而改变其性状的过程。目前还没有用来改良树木。通过基因改良，可能创造出具有产量高、生长快、抗逆强特点的树木。很大程度上，种植基因改良树木可以带来诸多益处。</p><p> <span word="First">First</span>, <span word="genetically">genetically</span> <span word="modified">modified</span> <span word="trees">trees</span> <span word="are">are</span> <span word="designed">designed</span> <span word="to">to</span> <span word="be">be</span> <span word="hardier">hardier</span> <span word="than">than</span> <span word="nature">nature</span> <span word="trees">trees</span>; <span word="that">that</span> <span word="it">it</span>, <span word="they">they</span> <span word="are">are</span> <span word="more">more</span> <span word="likely">likely</span> <span word="to">to</span> <span word="survive">survive</span> <span word="than">than</span> <span word="their">their</span> <span word="unmodified">unmodified</span> <span word="counterparts">counterparts</span>. <span word="In">In</span> <span word="Hawaii">Hawaii</span>, <span word="for">for</span> <span word="example">example</span>, <span word="a">a</span> <span word="new">new</span> <span word="pest">pest</span>-<span word="resistant">resistant</span> <span word="species">species</span> <span word="of">of</span> <span word="papaya">papaya</span> <span word="tree">tree</span> <span word="has">has</span> <span word="been">been</span> <span word="developed">developed</span> <span word="in">in</span> <span word="response">response</span> <span word="to">to</span> <span word="ring">ring</span>-<span word="spot">spot</span> <span word="virus">virus</span> <span word="infections">infections</span> <span word="that">that</span> <span word="have">have</span> <span word="repeatedly">repeatedly</span> <span word="damaged">damaged</span> <span word="the">the</span> <span word="native">native</span> <span word="papaya">papaya</span>-<span word="tree">tree</span> <span word="population">population</span>. <span word="Planting">Planting</span> <span word="the">the</span> <span word="genetically">genetically</span> <span word="modified">modified</span> <span word="papayas">papayas</span> <span word="has">has</span> <span word="largely">largely</span> <span word="put">put</span> <span word="an">an</span> <span word="end">end</span> <span word="to">to</span> <span word="the">the</span> <span word="ring">ring</span>-<span word="spot">spot</span> <span word="problem">problem</span>.</p><p> 首先，基因改良树木设计得比天然树木更能承受不良环境。也就是说，相对于它们没有改良的同类，它们更易存活。比如，在夏威夷有一种新的抗虫害的番木瓜树。这种树可以抵抗环斑病毒的感染，而正是这种环斑病毒常常会降低当地番木瓜树的数量。种植这种基因改良的番木瓜可以很大程度上解决环斑病毒的问题。</p>
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