Unit 4 Global warming试卷|高中英语,人教版(新课程标准),必修5、选 ...
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IntroductionZebrafishhavetransparentembryosthatdevelopoutsidethemother.Theydeveloprapidly,sothatat24hoursafterfertilization,theembryohasformedmostofitstissueandorganprimordiaanddisplaysthecharacteristictadpole-likeform.Also,thecelldivisionoccuronlyintheanimalpoleblastodisc.Thesedivisionsarerapid,withaperiodicityofabout15minuteseach.Thefirst12divisionsoccursynchronously,formingamoundofcellsthatsitsattheanimalpoleofalargeyolkcell.Threekindofmovements(epiboly,involutionandconvergence)canbedistinguishedintheearlydevelopmentofzebrafishembryo.Involutionandconvergenceresultofmigrationofdeepcellsmovingpresumablyusingfibroblasts,butthemolecularnatureofthemechanismdrivingtheepibolyisnotknownyet.PreviousexperimentsshowedthatirrADIationofzebrafishzygoteswithultravioletlightselectivelyimpairsepibolyresultinginembryoswithopenblastoporesbutwell-formedanterioraxes.Theultravioletlighteffectisnotrestrictedtothezygotestageasirradiationoflaterembryonicstagesalsoimpairsepiboly.Theultraviolet-sensitivetargetmaythusbematernallyencodedcomponentsofthemachinerydrivingepiboly.Reference:U.StrahleandS.Jesuthasan,Development119,909-919(1993)
ObjectiveTheobjectiveofthisexperimentwastoexposeseveralembryosatdifferentlevelofUVirradiationandobservethepotentialmalformations.Selectionofembryos1)Embryoswerefertilizedonthemorning.2)Afterfertilization,weselectedseveralnewlyfertilizedzygoteswhichconsistofalargeregionrichwithyolkvesiclesandasmalleryolk-freeblastodisc.Weusedtheembryosjustbeforethe2-cellstage(firstcleavage). | 
| ProcedureforUVirradiation 1)Weput15embryos,randomlyorientedintheirchorionin3differentpetridishes.ToproducetheUVirradiationweuseda254nmCL-1000UVcrosslinker.TochangetheUVdoseswecanchangetheexposuretimes.Nevertheless,inthisexperimentweincreasedtheirradiationwithoutchangethetimeofexposure.2.)ExposureI(1.8mJ/cm2)Weplaced15embryosinapetridishandthenweputthepetridishesintheCL-1000UVcrosslinkerasexplainedpreviously.3)ExposureII(3.6mJ/cm2)Samethingbutthelevelofirradiationwasdoubled.4)Wealsoput15embryosinapetridishanddidnotirradiatedthem.Theyservedasreferenceduringtheobservation(thenextday).5)Weplacedthe3petridishestoincubateat28ºCinembryomedia. ResultsIntheearlydevelopment,therapidcleavagedivisionsarenotaffectedbytheUV-light.Anomaliesstartwhenepibolystarts.Treatedembryosprogressslowerthanuntreatedembryo.So,thefundamentalcomponentsdrivingtheepibolyshouldstarttoworkinthelatezygote.Theexperimentsgaverisetothreelevelofimpair: | | | 
| TypeA-->Slightlyaffected.Theblastodermhascoveredtheyolkcellupto80%andshowsawell-formedanterioraxisrudimentonthedorsalside. | | | TypeC-->Themoreaffected.TypeB-->Affected.RetardationofepibolybutdonotformTheblastodermroundedupformingavesicleonanaxisrudiment.topoftheyolkmass.Allthecontrolgaverisetonormalembryowithnormalepibolymovement.Asshownonthetable,theimportanceofthe"mutation"areproportionalwiththelevelofUVexposure.Theirradiatedembryosaredisorganizedandlessmicrotubuleswerefoundinthecytoplasmiclayeroftheyolksphere(Strahle).Thus,sinceepibolyistheonlyonemovementintheembryowhichisaffected,itshouldbedrivenbymotorsthatusemicrotubules. |
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