美国名人 女科学家 巴巴拉·麦克林托克.docx

美国名人女科学家巴巴拉麦克林托克BarbaraMcCIintockplaystopmutemaxvolume00:00-15:51repeatByGeorgeGrow2005-5-28(THEME)VOICEONE:mDougJohnson.VOICETWO:AndmBarbaraKleinwithPEOPLEINAMERICAinVOASpecialEnglish."Today,wetellaboutBarbaraMcClintock.Shewasoneofthemostimportantscientistsofthetwentiethcentury.Shemadeimportantdiscoveriesaboutgenesandchromosomes.(THEME)VOICEONE:BarbaraMcClintockwasborninnineteen-oh-twoinHartford,Connecticut.Barbarawasthethirdoffourchildren.HerfamilymovedtotheBrooklynareaofNewYorkCityinnineteen-oh-eight.Barbarawasanactivechildwithinterestsinsportsandmusic.Shealsodevelopedaninterestinscience.ShestudiedscienceatCornellUniversityinIthacazNewYork.Barbarawasamongasmallnumberofundergraduatestudentstoreceivetrainingingeneticsinnineteentwenty-one.Yearslater;shenotedthatfewcollegestudentswantedtostudygenetics.VOICETWO:Intheearlynineteen-twentieszgeneticshadnotreceivedwidespreadacceptanceasasubject.Onlytwentyyearshadpassedsincescientistsre-discoveredthetheoriesofheredity.GregorMendelproposedtheseideasaftercompletingaseriesofexperimentswithplants.Hisexperimentshelpedscientistsbetterunderstandhowgenesoperate.Theyshowedhowgeneticqualitiesarepassedtolivingthingsfromtheirancestors.VOICEONE:BarbaraMcClintockdecidedtostudybotany,thescientificstudyofplants,atCornellUniversity.Shecompletedherundergraduatestudiesinnineteentwenty-three.McClintockdecidedtocontinuehereducationatCornell.Shecompletedamaster'sdegreeinnineteentwenty-five.Twoyearslateshefinishedallherrequirementsforadoctoratedegree.Inthelatenineteen-twenties,McClintockjoinedseveralotherstudentsinagroupthatstudiedgenetics.ThestudentsincludedafuturewinneroftheNobelPrize,GeorgeBeadle.AnotherwasMarcusRhoades.Yearslater,hewouldbecomealeadingexpertingenetics.McClintocksaidbothmenrecognizedtheimportanceofexploringtheconnectionbetweengenesandchromosomes.McClintockstayedatCornellaftershecompletedhereducation.Shetaughtstudentsbotany.Shealsosupervisedgeneticstudiesofthecornplant,ormaize.Shestudiedchromosomes,whicharelinesofgenes.Shemadeseveraldiscoveriesaboutgenesandchromosomes.VOICETWO:ThenineteenthirtieswerenotagoodtimetobeayoungscientistintheUnitedStates.Thecountrywasinthemiddleofthegreateconomicdepression.MillionsofAmericanswereunemployed.Malescientistswereofferedjobs.Butfemalegeneticistswerenotmuchindemand.McClintockreceivedtwoofferstotravelandcarryoutresearchprojects.ThefirstcamefromAmerica'sNationalResearchCouncil.Sheworkedatseveralplaces,includingCornellandtheUniversityofMissouriinColumbia.Later,agroupcalledtheGuggenheimFoundationprovidedfinancialaidforhertostudyinGermany.McClintockwenttoBerlin,butreturnedtoCornellthefollowingyear.Herskillsandworkwerewidelypraised.Butshestillwasunabletofindapermanentjob.(MUSIC)VOICEONE:Foryears,scientistshadbeenusingx-raystostudygeneticmaterialinplantsandotherorganisms.Theyfoundthatx-rayscausedgenestochange.Sometimes,thex-raysphysicallybrokethechromosome.Geneticresearcherslookedforchangesintheorganism.Thentheyusedthisinformationtoproduceamaplinkingthechangestoasingleareaofthechromosome.McClintockbecameinterestedinthewaygenesreactedtounusualevents.SheformedasuccessfulworkingrelationshipwithLewisStadleroftheUniversityofMissouri.Hehaddemonstratedtheeffectsofx-raysoncorn.StadlersentmaizetreatedwithradiationtoMcClintock.Sheidentifiedunusualareasshecalledringchromosomes.Shebelievedtheywerechromosomesbrokenbyradiation.Thebrokenendssometimesjoinedtogetherandformedacircle,orring.Thisledhertobelievethatastructureattheendofthechromosomepreventschromosomesfromchanging.Shecalledthisstructurethetelomere.VOICETWO:StadlergottheUniversityofMissouritoofferapermanentpositiontoMcClintockinnineteenthirty-six.Shebecameanassistantprofessor.Duringhertimeattheuniversity,sheworkedwithplantstreatedwithx-rays.Shealsodiscoveredplantswithchromosomesthatbrokewithouthelpofradiation.Shedescribedthisactivityasthebreakage-fusion-bridgecycle.UniversityofficialsandprofessorsrecognizedtheimportanceofMcClintock'sresearch.Yetshebelievedthatshewasnotabletomakeprogressinherposition.SoshedecidedtoleavetheUniversityofMissouri.(MUSIC)VOICEONE:AnoldfriendfromCornell,MarcusRhoades,invitedMcCIincocktospendthesummerofnineteenforty-oneworkingattheColdSpringHarborLaboratory.ItisaresearchcenteronLongIsland,nearNewYorkCity.McClintockstartedinatemporaryjobwiththegeneticsdepartment.Ashorttimelater,sheacceptedapermanentpositionwiththelaboratory.Thisgaveherthefreedomtocontinueherresearchwithouthavingtoteachorrepeatedlyaskforfinancialaid.AtColdSpringHarborLaboratory,McClintockcontinuedherworkwiththebreakage-fusion-bridgecycle.Shefoundthatsomecornplantgenesactedinanunusualway.Theyappearedtomovefromcelltocellduringdevelopmentofcornparticles,orkernels.Shediscoveredthatthegenesmovedonandbetweenchromosomes.VOICETWO:McClintockconfirmedherdiscoveryandextendedherobservationsforsixyears.Thechangescouldnotbeexplainedbyanyknowntheory.So,shedevelopedherowntheory.Shebelievedthemoveablegeneswerenotgenesatall,butgeneticcontrollersorcontrollingelements.Shesaidtheyinfluencedtheactionsofothergenes.Duringthisperiod,McClintockwaselectedtotheNationalAcademyofSciences.Shewasthethirdwomaneversohonored.ShealsowasnamedpresidentoftheGeneticsSocietyofAmerica.VOICEONE:Innineteenfifty-one,McClintockwasaskedtopresentherfindingsataconferenceheldatColdSpringHarborLaboratory.Herreportdescribedthemovementofgenesfromonepartofachromosometoanother.Sheusedthepresentationtodiscussherideasofcontrollingelementsingenes.Theotherscientistsreactedtoherideaswithamixtureofcriticismandsilence.Mostscientistsbelievedthatgenesdidnotmove.Fewpeopleseemedtoacceptherfindings.Yetothersarguedthatherexperimentswerecomplexanddifficulttoexplain,eventootherscientists.Theysaidshewouldnothavebeeninvitedtospeakunlessconferenceorganizersunderstoodsomeoftheimportanceofherwork.(MUSIC)VOICETWO:Foryears,manyscientistsdismissedMcClintock'sfindings.Duringthisperiod,shecontinueddoingherownworkandreachingherownfindings.Beginninginthelatenineteen-fiftieszshewenttoCentralandSouthAmericatostudydifferentkindsofmaizeplants.Sheexaminedthedevelopmentofagriculturalmaizebynativepeoples.Shealsoassistedyoungerscientistsandstudentsingenetics.HerworkattheColdSpringHarborLaboratorywasrecognizedinnineteenseventy.ShewasgiventheAmericangovernment'shighestscienceaward-theNationalMedalofScience.VOICEONE:Bythenineteen-seventies,newlydevelopedmethodsofmolecularbiologyconfirmedwhatMcClintockhadlearnedthroughobservation.Herdiscoverieshavehadaneffectoneverythingfromgeneticengineeringtocancerresearch.McClintockwontheNobelPrizeforPhysiologyorMedicineinnineteeneighty-threeforherdiscoveryoftheabilityofgenestochangepositionsonchromosomes.ShewasthefirstAmericanwomantowinanunsharedNobelPrize.BarbaraMcClintockremainedatColdSpringHarborfortherestofherlife.Shediedinnineteenninety-two.Shewasninetyyearsold.(THEME)VOICETWO:ThisprogramwaswrittenbyGeorgeGrow.LawanDaviswasourproducer.mBarbaraKlein.VOICEONE:AndmDougJohnson.JoinusagainnextweekforPEOPLEINAMERICAinVOASpecialEnglish.