資源描述：
《【素材】Module 8 Unit 2素材》由會(huì)員上傳分享，免費(fèi)在線閱讀，更多相關(guān)內(nèi)容在應(yīng)用文檔-天天文庫(kù)。
1、Whatiscloning?Cloningmeanstheproductionofgeneticallyidenticalanimals.In1995scientistsattheRoslinInstituteinEdinburgh,ScotlandproducedMeganandMorag-twolambsclonedfromasingleembryo.In1996Dollythesheepwasproduced,thefirstexampleofacloneproducednotfromanembryocellbutfromacelltakenfromanadu
2、ltsheep.Shewasclonedusinganucleartransfertechnique,wherethenucleusfromacelltakenfromthemammaryglandofanadultsheepwasfusedwithanunfertilizedeggfromwhichthenucleushadbeenremoved.277cellswerefusedinthisway,resultingin29viableembryoswhichwereimplantedintosurrogateBlackfaceewes.Onegavebirth
3、toDolly.Dollydiedin2003aftersufferingthesignsofprematureageingsuchasarthritisandalivercomplaint.The'production'ofDollyhassparkedacloningfrenzy.1998sawthearrivalofcowsclonedusingthesametechniquethatproducedMeganandMorag1.TheRoslininstituteclonedthefirstpigin20002.IntheUSin2001arhesusmac
4、aquemonkeycalledTetrawascloned3.AlsointheUSin2002aclonedkittenwasreported4inthesameyearasthefirstclonedrabbitsinFrance5.In2003thefirstclonedmule6,horse7andrat8werereported.AnimalwelfareCloninginvolvesmanypossibilitiesfordetrimentaleffectsonanimals.Forexample,clonedlambsandcalvesarefreq
5、uentlyabnormallylargeatbirth-somehavebeentwicenormalsize.Onecloningexpertadmittedin1992that"manyclonedcalvesareabnormal".9InAustralia,alamboffivetimesthemeanbirthweightforthebreedhasbeenrecorded.Inaddition,clonedanimalsareoftenfoundtohavemalformedinternalorgans.10Bothoftheseadverseeffe
6、ctswereseeninthefirstEdinburghexperimentsin1995thatledtoMeganandMorag.Inadditiontodeaththroughmalformedinternalorgans,onelambhadtobedeliveredbycaesareansectionbecauseithadgrowntotwiceitsnormalsizeinthewomb,andallbutoneofthefiveclonedlambswereatleast20%largerthantheyshouldhavebeen.Immed
7、iatelyafterbirthmanyclonedlambshavebreathingdifficulties,arelethargicandoftenwillnotsuckle.Asaconsequence,perinatalmortalityishigh.Miscarriageratesarealsohigh;thisisthoughttobeatleastinpartbecauseof'largeoffspringsyndrome'.11Cloningtechniquesalsorequireagreatdealofsurgicalinterventio
