新托福TPO21综合写作训练详细解析：基因改良

　　阅读材料：

　　Genetic modification, a process used to change an organisms genes and hence its characteristics, is not being used to improve trees. Through genetic modification, it is possible to create trees that produce more fruit, grow faster, or withstand adverse conditions. Planting genetically modified trees on a large scale promises to bring a number of benefits.

　　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。

　　First, genetically modified trees are designed to be hardier than nature trees; that it, they are more likely to survive than their unmodified counterparts. In Hawaii, for example, a new pest-resistant species of papaya tree has been developed in response to ring-spot virus infections that have repeatedly damaged the native papaya-tree population. Planting the genetically modified papayas has largely put an end to the ring-spot problem.

　　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。

　　Moreover, genetically modified trees promise to bring a number of economic benefits to those who grow them. Genetically modified trees tend to grow faster, give greater yields of food, fruit, or other products and be hardier. This allows tree farmers to get faster and greater returns on their farming investment and save on pesticides as well.

　　而且，基因改良的树木据信可以给种植者带来巨大的经济利益。基因改良的树木基因改良更快。同时，产量更高，也就是说可以获得更多的粮食、水果以及其他产品。而且，这些树木抗逆性更好。这样就能是的弄明可以更多而且更多地收回投资，同时节约杀虫剂的花费。

　　Finally, the use of genetically modified trees can prevent overexploitation of wild trees. Because of the growing demand for firewood or building timber, many forests around the world are being cut down faster than they can be replaced. Introducing genetically modified trees designed for fast growth and high yield in given geographic conditions would satisfy the demand for wood in many of those areas and save the endangered native trees, which often include unique or rare species.

　　最后，种植基因改良树木可以减少对野生树木的过度开发。由于对于木柴和建筑木材的越来越大，世界上森林砍伐的速度超过了再生速度。引入在相同地里条件下生长更快、产量更大的改良树木可以很多地方对于木材的需求，这样可以保护那些独特而稀少的濒危野生树种。

　　阅读部分需要提取的观点是：

　　- Main point: 基因改良树木优点很多

　　- Sub point 1: 可以抵御病虫害

　　- Sub point 2: 可以提高农民的收入

　　- Sub point 3: 可以保护天然森林

　　听力材料：

　　Sure, there is benefit to planting genetically modified trees, but are these trees really as great as they first sound? When you examine the subjects closely, there are some serious problems and causes associated with the using of genetic modified trees.

　　当然，种植基因改良树木是有好处的，但是真的有利到可以作为首选作物吗？当你仔细审视这些理由的时候，就会发现基因改良树木会带来一些严重的问题。

　　First, genetically modified trees may be resistant to one particular condition, but it doesnt necessarily ensure their survival. You see: a typical non-modified tree population is genetically diverse. That means that for most threatening conditions, for climate, insects, and pests, whatever, there will be at least some individual trees of any given species tree that are resistant. So, even if the most of one kind of tree were killed, those few resistant ones will survive and ensure the survival of that species of tree. But, genetically modified trees are genetically much more uniform, so if there is supposed to an environmental challenge they have not been designed for, they will all die. So, if the climate changes or new pest engages in, the genetically modified trees will likely be completely wagged out.

　　首先，基因改良树木可能对某种特定问题有抵抗力，但是这却不足以保证它们的生存。你看，非基因改良的树木种群是具有基因多样性的。这就意味着无论何种树木，即便是在遭遇极端气候灾害或者虫害的情况下，都至少有部分个体对灾害有抵抗能力。所以，即便种群中的大多数都死亡了，那么少数有抵抗力的存活下来也能保证这个种群的延续。但是对于基因改良树木基因是一直的，所以当他们受到他们基因设计里不能低于的环境挑战时，他们会全部死亡。所以，当气候发生变化或者有新的害虫出现，那么基因改良树木就将全部死亡。

　　That is the second point. There are hidden causes associated with the growing genetically modified trees. You see, the company that genetically modified tree can charge tree farmers much more for its seeds than unmodified tree seeds would cost. Also, after youve grown the tree, you can not just collect the seeds and plant the new tree for free. By law, you have to pay the company every time you plant.

　　现在说第二点。在基因改良树木的生长过程中伴随着一些隐含问题。你看，公司都是以高于天然种子很多的价格向农民出售基因改良树木种子的。同时，你现在不能再每年收获之后收集种子，然后来年免费再种了。因为根据法律规定，你每年都必须向种子公司支付费用。

　　And finally, genetically modified trees might actually cause even more damage to the local wild trees. You see, genetically modified trees often grow more aggressively than natural trees do. And genetically modified trees are typically planted among natural trees. As a result, the genetically modified trees out compete the native trees for resources: sunlight, soil nutrition and water. Eventually, crowd out the nature trees.

　　最后，基因改良树木可能会对本土野生树木造成更多的损害。你看，基因改良树木相对于天然树木生长的更为迅猛。而且，基因改良树木一般来说跟天然树木是共同生长的。那么结果就是，基因改良树木会抢占天然树木的资源，诸如阳光、土壤和水等。慢慢地，基因改良树木就会挤走天然树木。

　　听力笔记内容：

　　Main point: 优点之中都存在问题

　　Sub point one: 如果遇到不能抵御的病虫害，可能会全部死亡

　　Sub point two: 会增加农民的成本，因为种子公司有权每年收费

　　Sub point three: 会损害天然森林，因为会争夺自然资源