【素材】Module 8 Unit 2素材

《【素材】Module 8 Unit 2素材》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。

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