关于克隆的英语文章

我留学时写的:

Haveyoueverwishedyoucouldhaveacloneofyourselftodohomeworkwhileyouhittheskateparkorwentoutwithyourfriends?Imagineifyoucouldreallydothat.Wherewouldyoustart?OnewordCloningareshowed.Whatiscloning?Cloningisthecreationofanorganismthatisanexactgeneticcopyofanother.ThismeansthateverysinglebitofDNAisthesamebetweenthetwo!Youmightnotbelieveit,buttherearehumanclonesamongusrightnow.Theyweren'tmadeinalab,though:they'reidenticaltwins,creatednaturally.Below,we'llseehownaturalidenticaltwinsrelatetomoderncloningtechnologies.

Researchadvancesoverthepastdecadehavetoldusthat,withalittlework,wehumanscanclonejustaboutanythingwewant,fromfrogstomonkeysandprobablyevenourselves!So,wecanclonethings,butwhywouldwewantto?Let'slookatsomeofthereasonspeoplegivetojustifycloning.

1.Cloningformedicalpurposes:

Ofallthereasons,cloningformedicalpurposeshasthemostpotentialtobenefitlargenumbersofpeople.Howmightcloningbeusedinmedicine?

•Cloninganimalmodelsofdisease

Muchofwhatresearcherslearnabouthumandiseasecomesfromstudyinganimalmodelssuchasmice.Often,animalmodelsaregeneticallyengineeredtocarrydisease-causingmutationsintheirgenes.Creatingthesetransgenicanimalsisatime-intensiveprocessthatrequirestrial-and-errorandseveralgenerationsofbreeding.Cloningtechnologiesmightreducethetimeneededtomakeatransgenicanimalmodel,andtheresultwouldbeapopulationofgeneticallyidenticalanimalsforstudy.

•Cloningstemcellsforresearch

Stemcellsarethebody'sbuildingblocks,responsiblefordeveloping,maintainingandrepairingthebodythroughoutlife.Asaresult,theymightbeusedtorepairdamagedordiseasedorgansandtissues.Researchersarecurrentlylookingtowardcloningasawaytocreategeneticallydefinedhumanstemcellsforresearchandmedicalpurposes.

•Pharmingfordrugproduction

Farmanimalssuchascows,sheepandgoatsarecurrentlybeinggeneticallyengineeredtoproducedrugsorproteinsthatareusefulinmedicine.Justlikecreatinganimalmodelsofdisease,cloningmightbeafasterwaytoproducelargeherdsofgeneticallyengineeredanimals.

2.RevivingEndangeredorExtinctSpecies

HaveyouseenJurassicPark?Inthisfeaturefilm,scientistsuseDNApreservedfortensofmillionsofyearstoclonedinosaurs.Theyfindtrouble,however,whentheyrealizethattheclonedcreaturesaresmarterandfiercerthanexpected.

Couldwereallyclonedinosaurs?

Intheory?Yes.Whatwouldyouneedtodothis?

•Awell-preservedsourceofDNAfromtheextinctdinosaur.

•Acloselyrelatedspecies,currentlyliving,thatcouldserveasasurrogatemother.

Inreality?Probablynot.It'snotlikelythatdinosaurDNAcouldsurviveundamagedforsuchalongtime.However,scientistshavetriedtoclonespeciesthatbecameextinctmorerecently,usingDNAfromwell-preservedtissuesamples.Foranexample,seeCanwereallycloneendangeredorextinctanimals?ontherightsideofthispage.

3.ReproducingaDeceasedPet

Nojoke!Ifyoureallywantedto,andifyouhadenoughmoney,youcouldcloneyourbelovedfamilycat.AtleastonebiotechnologycompanyintheUnitedStatesofferscatcloningservicesfortheprivilegedandbereaved,andtheyarenowworkingtoclonedogs.Butdon'tassumethatyourclonedkittywillbeexactlythesameastheoneyouknowandlove.

4.CloningHumans?

Tocloneornottoclone:thatisthequestion.Theprospectofcloninghumansishighlycontroversialandraisesanumberofethical,legalandsocialchallengesthatneedtobeconsidered.Whywouldanyonewanttoclonehumans?Somereasonsinclude:

•Tohelpinfertilecoupleshavechildren

•Toreplaceadeceasedchild

Althoughcloninghassomeadvantages,butontheotherhand,whenwehearofcloningsuccesses,welearnaboutonlythefewattemptsthatworked.Whatwedon'tseearethemany,manycloningexperimentsthatfailed!Andeveninthesuccessfulclones,problemstendtoariselater,duringtheanimal'sdevelopmenttoadulthood.Cloninganimalsshowsuswhatmighthappenifwetrytoclonehumans.Whathavetheseanimalstaughtusabouttherisksofcloning?

1.Highfailurerate

Cloninganimalsthroughsomaticcellnucleartransferissimplyinefficient.Thesuccessraterangesfrom0.1percentto3percent,whichmeansthatforevery1000tries,onlyoneto30clonesaremade.Oryoucanlookatitas970to999failuresin1000tries.That'salotofeffortwithonlyaspeckofareturn!

Whyisthis?Herearesomereasons:

•Theenucleatedeggandthetransferrednucleusmaynotbecompatible

•Aneggwithanewlytransferrednucleusmaynotbegintodivideordevelopproperly

•Implantationoftheembryointothesurrogatemothermightfail

•Thepregnancyitselfmightfail

2.Problemsduringlaterdevelopment

Clonedanimalsthatdosurvivetendtobemuchbiggeratbirththantheirnaturalcounterparts.ScientistscallthisLargeOffspringSyndrome(LOS).CloneswithLOShaveabnormallylargeorgans.Thiscanleadtobreathing,bloodflowandotherproblems.

BecauseLOSdoesn'talwaysoccur,scientistscannotreliablypredictwhetheritwillhappeninanygivenclone.Also,somecloneswithoutLOShavedevelopedkidneyorbrainmalformationsandimpairedimmunesystems,whichcancauseproblemslaterinlife.

3.Abnormalgeneexpressionpatterns

Arethesurvivingclonesreallyclones?Thecloneslookliketheoriginals,andtheirDNAsequencesareidentical.Butwillthecloneexpresstherightgenesattherighttime?

Inanaturally-createdembryo,theDNAisprogrammedtoexpressacertainsetofgenes.Lateron,astheembryoniccellsbegintodifferentiate,theprogramchanges.Foreverytypeofdifferentiatedcell-skin,blood,boneornerve,forexample-thisprogramisdifferent.

Incloning,thetransferrednucleusdoesn'thavethesameprogramasanaturalembryo.Itisuptothescientisttoreprogramthenucleus,liketeachinganolddognewtricks.Completereprogrammingisneededfornormalornear-normaldevelopment.Incompleteprogrammingwillcausetheembryotodevelopabnormallyorfail.

4.Telomericdifferences

Ascellsdivide,theirchromosomesgetshorter.ThisisbecausetheDNAsequencesatbothendsofachromosome,calledtelomeres,shrinkinlengtheverytimetheDNAiscopied.Theoldertheanimalis,theshorteritstelomereswillbe,becausethecellshavedividedmany,manytimes.Thisisanaturalpartofaging.

So,whathappenstothecloneifitstransferrednucleusisalreadyprettyold?Willtheshortenedtelomeresaffectitsdevelopmentorlifespan?

Whenscientistslookedatthetelomerelengthsofclonedanimals,theyfoundnoclearanswers.Chromosomesfromclonedcattleormicehadlongertelomeresthannormal.Thesecellsshowedothersignsofyouthandseemedtohaveanextendedlifespancomparedwithcellsfromanaturallyconceivedcow.Ontheotherhand,Dollythesheep'schromosomeshadshortertelomerelengthsthannormal.ThismeansthatDolly'scellswereagingfasterthanthecellsfromanormalsheep.

Todate,scientistsaren'tsurewhyclonedanimalsshowdifferencesintelomerelength.

Wehavetoassociatewithclonehumanwhenwehearcloning.Italsohasrisksanddisadvantages:

1.Healthrisksfrommutationofgenes-anabnormalbabywouldbeanightmarecometrue.Thetechniqueisextremelyriskyrightnow.Aparticularworryisthepossibilitythatthegeneticmaterialusedfromtheadultwillcontinuetoagesothatthegenesinanewbornbabyclonecouldbe-say-30yearsoldormoreonthedayofbirth.Manyattemptsatanimalcloningproduceddisfiguredmonsterswithsevereabnormalities.Sothatwouldmeancreatingclonedembryos,implantingthemanddestroying(presumably)thosethatlookimperfectastheygrowinthewomb.Howeversomeabnormalitiesmaynotappeartillafterbirth.Aclonedcowrecentlydiedseveralweeksafterbirthwithahugeabnormalityofbloodcellproduction..

Evenifafewclonedbabiesarebornapparentlynormalwewillhavetowaitupto20yearstobesuretheyarenotgoingtohaveproblemslater-forexamplegrowingoldtoofast.Everytimeacloneismadeitislikethrowingthediceandevenastringofhealthyclonesbeingbornwouldnotchangethelikelihoodthatmanyclonesborninfuturemayhaveseveremedicalproblems.Andofcourse,that'sjusttheonesborn.Whataboutallthedisfiguredandhighlyabnormalclonesthateitherspontaneouslyabortedorweredestroyed/terminatedbyscientistsworriedaboutthehorrorstheymightbecreating.

2.Emotionalrisks-achildgrowsupknowinghermotherishersister,hergrandmotherishermother.Herfatherisherbrother-in-law.Everytimehermotherlooksathersheisseeingherselfgrowingup.Unbearableemotionalpressuresonateenagertryingtoestablishhisorheridentity.Whathappenstoamarriagewhenthefatherseeshiswife'sclonegrowupintotheexactreplica(byappearance)ofthebeautiful18yearoldhefellinlovewith35yearsago?Asexualrelationshipwouldofcoursebewithhiswife'stwin,noincestinvolvedtechnically.

Ormaybethechildknowsitisthetwinofadeadbrotherorsister.Whatkindofpressureswillheorshefeel,knowingtheyweremadeasadirectreplacementforanother?ItisahumanexperimentdoomedtofailurebecausethechildwillNOTbeidenticalineveryway,despitethehopesoftheparents.Onehugereasonwillbethatthechildwillbebroughtupinahighlyabnormalhousehold:onewheregriefhasbeendivertedintomakingacloneinsteadofadjustingtoloss.Thefamilyenvironmentwillbetotallydifferentthanthattheothertwinexperienced.Thatitselfwillplacegreatpressuresontheemotionaldevelopmentofthechild.Youwillnotfindachildpsychiatristintheworldwhocouldpossiblysaythattherewillnotbeverysignificantemotionalrisktotheclonedchildasaresultofthesepressures.

3.Riskofabuseofthetechnology-whatwouldHitlerhavedonewithcloningtechnologyifavailableinthe1940s?Therearepowerfulleadersineverygenerationwhowillseektoabusethistechnologyfortheirownpurposes.Goingaheadwithcloningtechnologymakesthisfarmorelikely.Youcannothaveso-calledtherapeuticcloningwithoutreproductivecloningbecausethetechniquetomakeclonedbabiesisthesameastomakeaclonedembryototrytomakereplacementtissues.Andatthespeedatwhichbiotechisacceleratingtherewillsoonbeotherwaystogetsuchcells-adultstemcelltechnology.Itisrathercrudetocreateacompleteembryonicidenticaltwinembryojusttogetholdofstemcellstomake-say-nervoustissue.Muchbettertotakecellsfromtheadultandtriggerthemdirectlytoregresstoamoreprimitiveformwithouttheethicalissuesraisedbyinsertingafulladultsetofgenesintoanunfertilizedegg.

USPresidentBushsaid:Ibelieveallhumancloningiswrong,andbothformsofcloningoughttobebanned,forthefollowingreasons.First,anythingotherthanatotalbanonhumancloningwouldbeunethical.Researchcloningwouldcontradictthemostfundamentalprincipleofmedicalethics,thatnohumanlifeshouldbeexploitedorextinguishedforthebenefitofanother.Alsoinmyopinion,disadvantagesaremorethanadvantages.Cloningshouldbebanned.

Reference:

L,Sloman.2000,“MedicinalWorld”,ScienceandTechnology,Canberra.

Yoshukoo.2002,“HumanHealth”,CulturePublishion,Tokyo.

LiGuojing.2000,“MedicinalDevelopment”,MedicinalUniversityofChina,Beijing

Online:www.learningworld.org/medicinal/cloning.

Online:www.muc.edu.cn/worldnews/cloning.