首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
It is not often that biologists have a chance to watch natural selection in action. The best-known cases—the evolution of resist
It is not often that biologists have a chance to watch natural selection in action. The best-known cases—the evolution of resist
admin
2011-08-28
36
问题
It is not often that biologists have a chance to watch natural selection in action. The best-known cases—the evolution of resistance to antibiotics in bacteria and to pesticides in insects—are responses to deliberate changes people have made in the environment of the creatures concerned. But mankind has caused lots of accidental changes as well, and these also offer opportunities to study evolution.
Recently, two groups of researchers, one at New York University (NYU) and the other at the Woods Hole Oceanographic Institute in Massachusetts, have taken advantage of one of these changes to look at how fish evolve in response to environmental stress. The stress in question is pollution by polychlorinated biphenyls (PCBs). These chemicals—widely used in the middle decades of the 20th century to manufacture electrical insulation, coolants, sealants and plasticisers—often ended up dumped in lakes, rivers and coastal waters. Eventually, such dumping was banned (in America, this happened in 1977). But PCBs are persistent chemicals, and their effects are felt even today. In particular, they disrupt the immune systems of animals such as fish, cause hormonal imbalances and promote tumours.
As is the way of evolution, however, some fish species have developed resistance to PCB poisoning. Isaac Wirgin, at NYU, and Mark Hahn, at Woods Hole, have been studying PCB-re-sistant fish, to see how they do it. After that, the two researchers will be able to look at how these populations evolve yet again as the environment is cleaned up.
The species of interest to Dr Wirgin is the Atlantic tomcod of the Hudson river in upstate New York. Part of the Hudson was polluted with PCBs by two General Electric plants. Dr Hahn is looking at a different animal, the killifish, in New Bedford harbour, Massachusetts, which was polluted by other producers. Both Hudson tomcod and New Bedford killifish are able to tolerate levels of PCB far higher than those that would kill such fish in cleaner waters. The question is, why?
PCBs do their damage by binding to a protein called the aryl hydrocarbon receptor, or AHR, thus stopping it working properly. AHR is a transcription factor, meaning that it controls the process by which messenger molecules are copied from genes. These messenger molecules go on to act as the blueprints for protein production, so preventing a transcription factor from working can cause all sorts of problems. Both Hudson tomcod and New Bedford killifish, however, have unusual AHR molecules. And it is this that seems to explain their immunity.
A protein is a chain of chemical units called amino acids. In tomcods, AHR is composed of 1,104 such units. Except that in Hudson tomcod it frequently isn’t. These fish generally have 1,102 amino acids in their AHRs. The two missing links in the chain (a phenylalanine and a leucine, for aficionados) are encoded in the gene for ordinary tomcod AHR by six genetic "letters" that are missing from the DNA found in PCB-resistant Hudson tomcod. The shortened version of AHR does not bind nearly so easily to PCBs. It still, however, seems to work as a transcription factor. The result is fish that are more or less immune to PCB poisoning.
In the case of the New Bedford killifish the situation is similar, but more complicated. There are no missing amino acids. Dr Hahn has, however, found nine places along the amino-acid chain of killifish AHR where the link in the chain varies between individuals. Altogether, he has identified 26 such variations. Two of them seem particularly resistant to the effects of PCBs. It is not that the pollutants do not bind to the protein—they do. But the protein does not seem to mind. It appears to work equally well, whether or not it has PCB passengers on board.
These fishy cases are reminiscent of the peppered moth in Britain. This, too, evolved in response to industrial pollution. It developed black wings, so that it was invisible when it settled on soot-covered tree trunks. Now, with the clean air brought by anti-pollution legislation, British peppered moths are once again peppered.
Both the Hudson river and New Bedford harbour are being cleaned up, too. This year, for example, General Electric will dredge 1.8m cubic metres (2.4m cubic yards) of PCB-contaminated sediment out of 60km (35 miles) of the Hudson. Dredging will continue over the next few years, after which the river should be PCB-free. It is possible that the tomcod and the killifish will then evolve again, just as the peppered moth did, if their PCB-resistant proteins are not absolutely as good as the original versions—which they might not be, given that evolution did not find them before. If that happens, Dr Wirgin and Dr Hahn will be watching.
From The Economist, October 29, 2011
What’s the author’s intention by bringing the "peppered moth" up?
选项
A、To bring back the old memories of environmental protection.
B、To serve as a contrast to the Hudson river tomcod and New Bedford killifish.
C、To provide a prospect for the future evolution of the tomcod and the killifish.
D、To give a very good example of similar cases.
答案
C
解析
本题为推断题。作者在倒数第二段提到了白桦尺蛾也是随着工业污染而进化的。而现如今,空气变得清新了,白桦尺蛾也相应地恢复了原来的面貌。观察上下文,我们发现下文由此引申出清理哈德森河和新贝德福德港一事,并认为很有可能名为killifish的鳉鱼和名为tomcod的大西洋小鳕鱼也会相应进化。由此可以看出,选项C, “提出未来鳉鱼和大西洋小鳕鱼有可能进化的前景”正确。
转载请注明原文地址:https://kaotiyun.com/show/pvYO777K
0
专业英语八级
相关试题推荐
Inthepastfewyears,personalcomputers(PCs)havebecomebetter,strongerandfasterbutsohavethebitsandpiecesyouplug
Howtoliveto100Agrowingbodyofresearchsuggeststhatchronicillnessisnotaninevitableconsequenceofaging,butmo
In1969,theNationalWildlifeFederationbegantorecordanindexofenvironmentalqualitywhichmeasuresprogressordeclinei
In1969,theNationalWildlifeFederationbegantorecordanindexofenvironmentalqualitywhichmeasuresprogressordeclinei
ThefirstschoolIwenttowasared-brickbuildingontheedgeofthetown,inthedistrictofGeorgetown.Wehadasplendidte
Lastyear’seconomyshouldhavewontheOscarforbestpicture.Growthingrossdomesticproductwas4.1percent;profitssoared
Inbusiness,manyplacesadoptacreditsystem,whichdatesbacktoancienttimes.Atpresent,purchasescanbemadebyusingc
Intheatmosphere,carbondioxideactsratherlikeaone-waymirror--theglassintheroofofagreenhousewhichallowsthesun’
Fromthehealthpointofviewwearelivinginamarvelousage.Weareimmunizedfrombirthagainstmanyofthemostdangerousd
A、Itgivesconventionalaccountformedicine.B、Itintroducesthedietaryregimeforthesick.C、Itseesvariousmedicalissues
随机试题
________是公证活动的核心原则。
A.镜面舌B.草莓舌C.牛肉舌D.地图舌E.毛舌猩红热患者常出现【】
流行性腮腺炎最主要的病理特征
美国某公司于2004年12月1日在美国就某口服药品提出专利申请并被受理,2005年5月9日就同一药品向中国专利局提出专利申请,要求享有优先权并及时提交了相关证明文件。中国专利局于2008年4月1日授予其专利。关于该中国专利,下列哪一选项是正确的?(2008
下列属于一般存单纠纷案件依据的凭证有()。
精神分析理论在20世纪()年代成为临床社会工作的主导。
下列诗句按其所描写节日的先后顺序.排列正确的是:①桃符呵笔写,椒酒过花斜②九日黄花酒,登高会昔闻③粽包分两髻,艾束著危冠④马上逢寒食,途中属暮春
结合材料,回答问题:要坚持走中国特色社会主义政治发展道路和推进政治体制改革。要把制度建设摆在突出位置,充分发挥我国社会主义政治制度优越性,积极借鉴人类政治文明有益成果,绝不照搬西方政治制度模式。政治体制改革是我国全面改革的重要组成部分。
下面是PCI类总线的有关叙述,其中正确的是()
TheSeattleTimesCompanyisonenewspaperfirmthathasrecognizedtheneedforchangeanddonesomethingaboutit.Inthenews
最新回复
(
0
)