-学高中英语unitcloningwhatiscloning素材新人教版选修

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

2、eep.Shewasclonedusinganucleartransfertechnique,wherethenucleusfromacelltakenfromthemammaryglandofanadultsheepwasfusedwithanunfertilizedeggfromwhichthenucleushadbeenremoved.277cellswerefusedinthisway,resultingin29viableembryoswhichwereimplantedintosurrogateBlackfaceewes.OnegavebirthtoDolly.

3、Dollydiedin2003aftersufferingthesignsofprematureageingsuchasarthritisandalivercomplaint.The'production'ofDollyhassparkedacloningfrenzy.1998sawthearrivalofcowsclonedusingthesametechniquethatproducedMeganandMorag1.TheRoslininstituteclonedthefirstpigin20002.IntheUSin2001arhesusmacaquemonkeyca

4、lledTetrawascloned3.AlsointheUSin2002aclonedkittenwasreported4inthesameyearasthefirstclonedrabbitsinFrance5.In2003thefirstclonedmule6,horse7andrat8werereported.AnimalwelfareCloninginvolvesmanypossibilitiesfordetrimentaleffectsonanimals.Forexample,clonedlambsandcalvesarefrequentlyabnormally

5、largeatbirth-somehavebeentwicenormalsize.Onecloningexpertadmittedin1992that"manyclonedcalvesareabnormal".9InAustralia,alamboffivetimesthemeanbirthweightforthebreedhasbeenrecorded.Inaddition,clonedanimalsareoftenfoundtohavemalformedinternalorgans.10Bothoftheseadverseeffectswereseeninthefirs

6、tEdinburghexperimentsin1995thatledtoMeganandMorag.Inadditiontodeaththroughmalformedinternalorgans,onelambhadtobedeliveredbycaesareansectionbecauseithadgrowntotwiceitsnormalsizeinthewomb,andallbutoneofthefiveclonedlambswereatleast20%largerthantheyshouldhavebeen.Immediatelyafterbirthmanyclon

7、edlambshavebreathingdifficulties,arelethargic3andoftenwillnotsuckle.Asaconsequence,perinatalmortalityishigh.Miscarriageratesarealsohigh;thisisthoughttobeatleastinpartbecauseof'largeoffspringsyndrome'.11Cloningtechniquesalsorequireagreatdealofsurgicalinterventi