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1Unit2克隆：它将把我们引向何方？Cloninghasalwaysbeenwithusandisheretostay.Itisawayofmakinganexactcopyofanotheranimalorplant.Ithappensinplantswhengardenerstakecuttingsfromgrowingplantstomakenewones.Italsohappensinanimalswhentwinsidenticalinsexandappearanceareproducedfromthesameoriginalegg.Thefactisthatthesearebothexamplesofnaturalclones.克隆一直与我们同在，而如今它还要持续下去。这是一种用来生产与原型完全相同的动植物的方法。当园艺师从生长着的植物上剪下枝条来培植新植物时，就会产生这种现象。这种现象也发生在动物身上，从同一个原生卵子产生性别和相貌相同的双胞胎也是克隆。实际上，这些都是自然克隆现象。Cloninghastwomajoruses.Firstly,gardenersuseitallthetimetoproducecommercialquantitiesofplants.Secondly,itisvaluableforresearchonnewplantspeciesandformedicalresearchonanimals.Cloningplantsisstraightforwardwhilecloninganimalsisverycomplicated.Itisadifficulttasktoundertake.Manyattemptstoclonemammalsfailed.Butatlastthedeterminationandpatienceofthescientistspaidoffin1996withabreakthrough-thecloningofDollythesheep.Theprocedureworkslikethis:克隆技术有两大用途。第一，园艺师一直用它生产大量的供商用的植物；第二，它在对新植物物种的研究以及对动物的医学研究方面都是很有价值的。克隆植物简单，但克隆动物就比较复杂了，是一项很难完成的任务。克隆哺乳动物的多次尝试都失败了。但是，科学家的决心和耐心最终得到了回报，这就是1996年具有突破性的克隆羊“多莉”的诞生。它的程序如下图所示：21．母羊(A)提供一个卵细胞。2．在卵细胞中取出细胞核。3．卵细胞准备接受新的细胞核。4．母羊(B)提供一个供克隆的躯干细胞。该细胞核应包含生产一头新羊所需要的全部基因。5．取出该细胞的细胞核。6．用电把母羊(B)的躯干细胞核和母羊(A)的卵细胞结合起来。7．细胞分裂并生长成胚胎。8．把胚胎植入另外一头母羊(C)体内，母羊(C)就是克隆羊的代孕者。9．这头小羔羊就是母羊(B)所提，供的细胞核克隆而成的。Ontheonehand,thewholescientificworldfollowedtheprogressofthefirstsuccessfulclone,Dollythesheep.Thefactthatsheseemedtodevelopnormallywasveryencouraging.ThencamethedisturbingnewsthatDollyhadbecomeseriouslyill.CloningscientistswerecastdowntofindthatDolly'sillnessesweremoreappropriatetoamucholderanimal.AltogetherDollylivedsixandahalfyears,halfthelengthofthelifeoftheoriginalsheep.Sadlythesamearbitraryfateaffectedotherspecies,suchasclonedmice.Thequestionsthatconcernedallscientistswere:Wouldthisbeamajordifficultyforallclonedanimals?Wouldithappenforever?Coulditbesolvedifcorrectionsweremadeintheirresearchprocedure?一方面，整个科学界都在关注着首例成功的克隆动物多莉羊的成长¨多莉看来是在正常地成长着，这很令人鼓舞。接着传来了多莉病重的坏消息。研究克隆的科学家发现多莉得的病更容易发生在年老的羊身上．这让他们很沮丧。多莉总共只存活了六年半，这是它的原型羊寿命的一半。可悲的是，同样无法控制的命运也在影响着其他物种，如克隆鼠。科学家的脑海里产生的问题是：“这是不是所有克隆动物的一个主要困难呢？这种现象会不会永远发生？如果改进程序，问题会不会解决？Ontheotherhand,Dolly'sappearanceraisedastormofobjectionsandhadagreatimpactonthemediaandpublicimagination.Itbecamecontroversial.Itsuddenlyopenedeverybody'seyestothepossibilityofusingcloningtocureseriousillnessesandeventoproducehumanbeings.另一方面，多莉的出生引起了一阵强烈的反对，对，对媒体和公众的想象力也产生了巨大的影响。它引起了争议，因为它突然打开了人们的眼界，看到了有可能：用克隆技术来治疗重病，甚至克隆出人类。Althoughatpresenthumaneggcellsandembryosneededforcloningresearcharedifficulttoobtain,newspaperswroteofevilleadershopingtoclonethemselvestoattaintheirambitions.Religiousleadersalsoraisedmoralquestions.Governmentsbecamenervousandmoreconservative.Somebegantoreformtheirlegalsystemsandforbaderesearchintohumancloning,butothercountrieslikeChinaandtheUK,continuedtoaccumulateevidenceoftheabundantmedicalaidthatcloningcouldprovide.However,scientistsstillwonderwhethercloningwillhelporharmusandwhereitisleadingus尽管目前供克隆研究的人体卵细胞和胚胎还很难得到，但报纸报道说，有些邪恶头目希望把自己克隆出来以实现他的野心。宗教领袖也提出了道德方面的问题。各国政府惶恐不安而且更加谨慎，有些政府开始改革司法制度，明令禁止进行克隆人类的研究。但是其他国家如中国和英国，则还在继续收集克隆技术有可能提供丰富有的医疗救助的证据。然而，科学察们仍对克隆技术有助于人类还是有害于人类，以及克隆技术将把我们引向何处困惑。3UsingLanguageThepossibilityofcloningfierceandextinctwildanimalshasalwaysexcitedfilmmakers.Andtheyarenottheonlyones!ThepopularityoffilmssuchasJurassicPark,inwhichascientistclonesseveralkindsofextinctdinosaurs,proveshowtheideastruckamixtureoffearandexcitementintopeople'shearts.Butinfactwearealongwayfrombeingabletocloneextinctanimals.Scientistsarestillexperimentingwithcloningmammals.Thisisbecausethecloningofmammalsisstillanewscienceanditsstoryonlybeganseriouslyinthe1950sasthislistshows:1950scloningoffrogs1996firstcloneofamammal:Dollythesheep1970sresearchusingtheembryosofmice2000cowgavebirthtoabison1979workonembryosofsheepandmice2001China'sfirstclonedtwincalves1981firstexperimentalclonesofmice2002firstclonedcats1983firstexperimentalclonesofcows2005firstcloneddog…Fromtimetotimepeoplesuggestthatextinctanimalslikedinosaurs,canpossiblybebroughtbacktolifethroughcloning.Unfortunately,withwhatweknownow,thisiseitherimpossibleorunsuitable.Therearemanyreasons.◎TheinitialrequirementisthatyouneedperfectDNA(whichgivesinformationforhowcellsaretogrow).◎Alleffortsofcloningananimalwillbeinvainifthereisnotenoughdiversityinthegrouptoovercomeillnesses.Diversityinagroupmeanshavinganimalswiththeirgenesarrangedindifferentways.Theadvantageisthatifthereisanewillnesssomeoftheseanimalsmaydie,butotherswillsurviveandpassontheabilitytoresistthatdiseasetothenextgeneration.Thegreatdrawbacktocloningagroupofanimalsisthattheywouldallhavethesamearrangementofgenesandsomightdieofthesameillness.Thennoneofthemwouldbelefttocontinuethespecies.◎Itwouldbeunfairtocloneanyextinctanimalsiftheyweretoliveinazoo.Asuitablehabitatwouldbeneededforthemtoleadanaturallife.Basedonwhatweknownow,youcannotcloneanimalsthathavebeenextinctlongerthan10,000years.Actually,dinosaursdisappeared65,000,000yearsago.Sothechanceofdinosaurseverreturningtotheearthismerelyadream.WorkbookTopic:Shouldmedicalcloningbeallowed?Tea