高中英语 unit 2 cloning what is cloning素材 新人教版选修8

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1、Whatiscloning?Cloningmeanstheproductionofgeneticallyidenticalanimals.In1995scientistsattheRoslinInstituteinEdinburgh,ScotlandproducedMeganandMorag-twolambsclonedfromasingleembryo.In1996Dollythesheepwasproduced,thefirstexampleofacloneproducednotfromanembryocel

2、lbutfromacelltakenfromanadultsheep.Shewasclonedusinganucleartransfertechnique,wherethenucleusfromacelltakenfromthemammaryglandofanadultsheepwasfusedwithanunfertilizedeggfromwhichthenucleushadbeenremoved.277cellswerefusedinthisway,resultingin29viableembryoswhi

3、chwereimplantedintosurrogateBlackfaceewes.OnegavebirthtoDolly.Dollydiedin2003aftersufferingthesignsofprematureageingsuchasarthritisandalivercomplaint.The'production'ofDollyhassparkedacloningfrenzy.1998sawthearrivalofcowsclonedusingthesametechniquethatproduced

4、MeganandMorag1.TheRoslininstituteclonedthefirstpigin20002.IntheUSin2001arhesusmacaquemonkeycalledTetrawascloned3.AlsointheUSin2002aclonedkittenwasreported4inthesameyearasthefirstclonedrabbitsinFrance5.In2003thefirstclonedmule6,horse7andrat8werereported.Animal

5、welfareCloninginvolvesmanypossibilitiesfordetrimentaleffectsonanimals.Forexample,clonedlambsandcalvesarefrequentlyabnormallylargeatbirth-somehavebeentwicenormalsize.Onecloningexpertadmittedin1992that"manyclonedcalvesareabnormal".9InAustralia,alamboffivetimest

6、hemeanbirthweightforthebreedhasbeenrecorded.Inaddition,clonedanimalsareoftenfoundtohavemalformedinternalorgans.10BothoftheseadverseeffectswereseeninthefirstEdinburghexperimentsin1995thatledtoMeganandMorag.Inadditiontodeaththroughmalformedinternalorgans,onelam

7、bhadtobedeliveredbycaesareansectionbecauseithadgrowntotwiceitsnormalsizeinthewomb,andallbutoneofthefiveclonedlambswereatleast20%largerthantheyshouldhavebeen.Immediatelyafterbirthmanyclonedlambshavebreathingdifficulties,arelethargicandoftenwillnotsuckle.Asacon

8、sequence,perinatalmortalityishigh.Miscarriageratesarealsohigh;thisisthoughttobeatleastinpartbecauseof'largeoffspringsyndrome'.11Cloningtechniquesalsorequireagreatdealofsurgicalinterventio