Module5CloningPartTwo:TeachingResources第二部分：教学资源Section2:BackgroundinformationforModule5Cloning1.WhatisCloning?Haveyoueverwishedyoucouldhaveacloneofyourselftodohomeworkwhileyouhittheskateparkorwentoutwithyourfriends?Imagineifyoucouldreallydothat.Wherewouldyoustart?●Whatexactlyiscloning?Cloningisthecreationofanorganismthatisanexactgeneticcopyofanother.ThismeansthateverysinglebitofDNAisthesamebetweenthetwo!Youmightnotbelieveit,buttherearehumanclonesamongusrightnow.Theyweren'tmadeinalab,though:they'reidenticaltwins,creatednaturally.Below,we'llseehownaturalidenticaltwinsrelatetomoderncloningtechnologies.●Howiscloningdone?YoumayhavefirstheardofcloningwhenDollytheSheepshoweduponthescenein1997.CloningtechnologieshavebeenaroundformuchlongerthanDolly,though.Howdoesonegoaboutmakinganexactgeneticcopyofanorganism?Thereareacoupleofwaystodothis:artificialembryotwinningandsomaticcellnucleartransfer.Howdotheseprocessesdiffer?(1)ArtificialEmbryoTwinningArtificialembryotwinningistherelativelylow-techversionofcloning.Asthenamesuggests,thistechnologymimicsthenaturalprocessofcreatingidenticaltwins.OpenlargeversionInnature,twinsoccurjustafterfertilizationofaneggcellbyaspermcell.Inrarecases,whentheresultingfertilizedegg,calledazygote,triestodivideintoatwo-celledembryo,thetwocellsseparate.Eachcellcontinuesdividingonitsown,ultimatelydevelopingintoaseparateindividualwithinthemother.Sincethetwocellscamefromthesamezygote,theresultingindividualsaregeneticallyidentical.Artificialembryotwinningusesthesameapproach,butitoccursinaPetridishinsteadofinthemother'sbody.Thisisaccomplishedbymanuallyseparatingaveryearlyembryointoindividualcells,andthenallowingeach用心爱心专心116号编辑celltodivideanddeveloponitsown.Theresultingembryosareplacedintoasurrogatemother,wheretheyarecarriedtotermanddelivered.Again,sincealltheembryoscamefromthesamezygote,theyaregeneticallyidentical.(2)SomaticCellNuclearTransferSomaticcellnucleartransfer,(SCNT)usesadifferentapproachthanartificialembryotwinning,butitproducesthesameresult:anexactclone,orgeneticcopy,ofanindividual.ThiswasthemethodusedtocreateDollytheSheep.WhatdoesSCNTmean?Let'stakeitapart:Somaticcell:Asomaticcellisanycellinthebodyotherthanthetwotypesofreproductivecells,spermandegg.Thesearealsocalledgermcells.Inmammals,everysomaticcellhastwocompletesetsofchromosomes,whereasthegermcellsonlyhaveonecompleteset.Nuclear:Thenucleusislikethecell'sbrain.It'sanenclosedcompartmentthatcontainsalltheinformationthatcellsneedtoformanorganism.ThisinformationcomesintheformofDNA.It'sthedifferencesinourDNAthatmakeeachofusunique.Transfer:Movinganobjectfromoneplacetoanother.TomakeDolly,researchersisolatedasomaticcellfromanadultfemalesheep.Next,theytransferredthenucleusfromthatcelltoaneggcellfromwhichthenucleushadbeenremoved.Afteracoupleofchemicaltweaks,theeggcell,withitsnewnucleus,wasbehavingjustlikeafreshlyfertilizedzygote.Itdevelopedintoanembryo,whichwasimplantedintoasurrogatemotherandcarriedtoterm.Thelamb,Dolly,wasanexactgeneticreplicaoftheadultfemalesheepthatdonatedthesomaticcellnucleustotheegg.Shewasthefirst-evermammaltobeclonedfromanadultsomaticcell.用心爱心专心116号编辑
