mechanisms of mitosis - bio.miami.edu · the cells you count should be round or cuboidal and...
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MechanismsofMitosisPracticingtheExperimentalProcedures
Todiscoverhowchromosomesmoveinadividingcell,yourteamwillexaminetheoutcomeoftreatingarapidlydividingtissue(onionroottip)withasubstancethateitherpromotes(Indole-3_butyricacid)mitosisorinhibits(trifluralin)mitosis.Todayyouwilllearnandpracticethetechniquesyoumustmasterinordertoanalyzemitoticcells.
I.PreparationforLabProceduresBeforeyoubegin,youmustcompleteimportantpreparations.
Beforeyoubegin…1.DonyourPersonalProtectiveEquipment(PPE)!
• Gloves• Labcoat• Safetygoggles• Otherprotectivegear
2.Labelallmaterials(beakers,onionplants,microscopeslides)appropriately.Itiscriticallyimportanttolabeleverythingproperly.
3.Forbestresultsandeaseofcounting,cleanmicroscopeslideswell.
• Place1-3dropsof95%ethanolontheslide• WipewellwithaKimwipe.• Dothisonbothsidesoftheslide• Repeat,asnecessary,untiltheslideisveryshinyandclear.
II.ChromosomeSquashProcedureForourpracticerun,onionroottipshavebeenincubatedinplainwater.Tovisualizechromosomesinthephasesofmitosis,youwillprepareandstaintheminaprocedureknownasachromosomesquash.
Becausesomereagentswewillusemaybesomewhatcaustic,youmustwearthenitrileglovesprovidedandyourownsafetyglasseswhileyouperformthechromosomesquash.Wearalabcoatorlabaprontoprotectyourclothesfromstaining.
Onionbulbswillsproutrootsiftheyareplacedinwaterforseveraldays(Figure1).Theonionsyouwillusetodayhadalloldrootsremovedapproximatelythreedaysbeforeyourlabsession.Thebulbswerethenimmediatelyplacedinplainwaterandallowedtosproutnewrootstoensurethepresenceoffresh,growingroottips.
Theonionroottipcellcycleisabout24hours.Thusitmaytakeapproximately24hoursofincubationwithanyparticularreagentbeforeonecanexpecttoseeanyeffectonmitoticcells.
Figure1.Sproutinggreenonions(scallions),Alliumsp.
Plantmitosisoccursinmeristemcellsatthetipsofrootsandshoots.Thesecandifferentiateintoanyothertypeofcell.
Theapicalmeristemisaboutonemillimeterfromtheapparenttipoftheroot(therootcap,composedofdeadcells)(Figure2a).
Forsafetyreasons,studentswillnotcutroots.Yourlabinstructorwillgivethemtoyou.
1.Obtainanonionrootfromyourlabinstructor.Theroottipisdelicate,anddesiccateseasily.
• Keeptheonionrootwetatalltimes!• Donotleaveonionrootsoutofthewaterorlyingonthelabbench.
Figure 2a. Onion root tip anatomy. Only the cells at theverytipoftheroot(ZoneofCellDivision)areundergoingmitosis. These are visually distinct in a fresh root tip,appearingmoreroundor square than theelongatedcellsintheZoneofElongationaboveit.
Figure2b. Roottipofcorn(Zeamays). Notethe clear appearance of the root cap. Justabove it is theapicalmeristemandtheZoneof Cell Division. The darker, longitudinallines above the cell division zone mark thenewlyformedvascularcambium.
2.Placetherootonanappropriatelylabeledslide.
3.Usingthedissectingscope,identifytheroottip.
• Long,rectangularcellsabovetheroottiparenolongerundergoingmitosis.• Donotincludenon-mitoticcellsinyoursquashorcounts.• Withasharprazorblade,cutoffonlythemeristematicregionoftheroottip.
4.Withfine-tippedforceps,placetheroottipwithapicalmeristemintoa1.5mlmicrocentrifugetube.(Forcepstipsarefragile.Handlewithcare.)
5.Fillthemicrocentrifugetubehalfwaywith1MHCl(dropperbottleonyourlabbench)Thiswillsoftentheconnectionbetweenthecells.Usecaution:HClisastrongacid.
6.LABELTHETUBEwithaSharpiemarker.
7.Closethetubeandplaceitinahot60°Cwaterbathforexactly8minutes.(Toolonginhotacidyieldsasoggymassofcellsthatwilldisintegratewhenyourinse).
8.Carefullyremovethetubefromthehotbath.
9.Toremovethe1MHCl,fillthetubewithdeionized(DI)water,andthensuctionitoutwithaplasticsqueezepipet.Repeatthisprocedureforatotalofthreerinses.
Placeallremovedwastewaterintothecontaineratyourstationlabeled"WASTESOLUTIONS".
Nothinggoesintothesinksortrashcans!
10.Add2dropsof0.5%toluidinebluetothetube.
11.Incubateatroomtemperaturefor5minutesGentlyflickthetubewithyourfingernailaboutonceperminutetodistributethestain.Makesuretheroottipstaysinthestain.
12.RinsetheexcesstoluidineblueasyoudidfortheHCl.
a) FillthetubewithDIwater,thenremoveitwiththeplasticsqueezepipet.b) Repeatatotalofthreetimesc) Removealmostallofthelastrinse.d) Useadissectingprobetogentlypushtheroottipontoaclean,labeledslide.
Bythetimeyouhaveremovedthelastbitofrinsewater,youshouldbeabletoseeyourblueroottipclearly
13.AddonedropofDIwatertotheroottipontheslide.Gentlydropacoverslipoverit.
14.Placeasheetofbibulouspaper(bookletsuppliedonyourtray)overthecoverslip.
• Gentlypressstraightdownontothecoverslipwithroottipunderneath.• Becarefulnottobreakthecoverslip,oryou’llhavetostartover.
DONOTPLACEYOURSLIDEINSIDETHEBIBULOUSPAPERBOOKLET!Keepthepagescleananduncontaminatedforyourfutureslidepreps.
15.Removeanddiscardthebibulouspaper.
16.Placetheslideonyourcompoundmicroscopestage.ALWAYSBEGINMICROSCOPEOBSERVATIONSONLOWPOWER.
a) Findandfocusonyourroottipcellsintheviewingfieldonlowpower.b) Swiveltheobjectivetothenexthigherobjective,andfocusagain.c) Dothisuntilyouareproperlyfocusedwiththe40Xobjective,whichyouwillneedtousetoseenuclearmaterialclearly.
17.Examineyoursquash.Youshouldbeabletoseecellsinvariousstagesofmitosis.III.DataCollectionChooseaproperlysquashedareaandcountallofthecellsyoucansee(~50-200cells).Thecellsyoucountshouldberoundorcuboidalandflattenedintoasinglecelllayer.Donotcountlong,rectangularcells,asthesearenolongerundergoingmitosis.
SeeFigure4foranexampleofwhatyoushouldexpecttoseeinyourslides.
Figure4a.Alliumroottipcellsundergoingmitosis(acetocarminestain).http://upload.wikimedia.org/wikipedia/commons/d/d3/Onion_root_mitosis.jpg
Figure4b.Yourpreparationwillprobablylooksomethinglikethis.Yellowarrowsindicatecellsinvariousstagesofmitosis.(preparationandphotocourtesyofLindaWhite)
Countcellsinfourdifferentfieldsofviewforeachroottip.Thiswillgiveyouagoodsamplefromanindividualonion(about100-300cellsperroottip,dependingonitssizeandquality).
Record• thetotalnumberofcellsyoucanidentify• thetotalnumberofcellsinanystageofactivemitosis• thetotalnumberofcellsinEACHstageofthecellcycle
(1)interphase(2)prophase(3)metaphase(4)anaphase(5)telophase
onesample=allthecellscountedinonerootfromoneonion
AvoidPseudoreplication
• Donottakemultiplerootsfromthesameonion• Donotcountmultiplefieldsofviewasseparateexperimentalsamples.
Allcellscountedfromasingleonionplantcompriseonesample.Asingleindividualonion’sroottipsareallpartofthesameorganism.Countingthemasseparatesamplescreatesfalsereplication.IV.DataAnalysis:MitoticIndicesAMitoticIndex(M)isameasureoftheproportionofmitoticcellsinasampledcellpopulation.
M=nm/Nnm=totalnumberofmitoticcellsinthesampleN=totalnumberofcellscountedinthesample
Foreachofyoursamples,calculateandrecordaMitoticIndex,andrecordthesevaluesinatableliketheoneshown.Provideanappropriatelegendforthetable.AMitoticPhaseIndex(MP)isameasureoftheproportionofcellsinaparticularphaseofmitosisinasampledpopulationofmitoticcells.
MP=np/nm
np=#ofcellsinprophaseinthesamplenm=totalnumberofmitoticcellsinthesample
(Theequationaboveshowstheindexforprophase,butitcanbeusedforanyphase.)
Enteryourdatainatablesuchastheoneshownbelow,andprovideanappropriatelegendthatclearlydescribesthesourceofthedataandcontentsofthetable.Table1. Sample#
MitoticIndex(M)
ProphaseIndex(Mp)
MetaphaseIndex(Mm)
AnaphaseIndex(Ma)
TelophaseIndex(Mt)
Whenyourteamcollectsdatafromtreatedanduntreated(control)onionsforyourresearchproject,youwillperformessentiallythesameprotocolsyouhavepracticedhere.Youwillalsodecidewhichindicestocalculateandreporttobestreflectyourobservations.Whenyouarecompletelyfinishedwithaslidepreparation,placeitintheBrokenGlassDisposalContaineratthefrontofthelabroom.Uponcompletionofalloftoday’sexercises,notifyyourlabinstructor,whowilltheninspectyourstationforcleanliness.Ifthestationisnotproperlycleanedandrestoredtoitsoriginalcondition,youmustcorrectthatbeforeyouleavethelab.
Teamsleavinganuntidylabstation,includingundisposedslides,trash,orothermaterials,willbedocked5points.