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DevelopmentalBiologyIntroductionofsomemodelorganismsModelOrganisms•Outofover1millionanimalspecies,moderndevelopmentalbiologyhasfocusedonaverysmallnumberwhichareofterdescribedas'modelorganisms'.•Themotivationfortheirstudyisnottounderstandjusthowthatparticularanimaldevelops,buttouseitasanexampleofhowallanimalsdevelop.•Muchdevelopmentalbiologyresearchissupportedbymedicalresearchfundingbodiesandtheirultimategoalitstounderstandhowthehumanbodydevelops,evenifthisisnottheimmediategoaloftheinvestigatorsthemselves.Caenorhabditiselegans•Caenorhabditiselegansisasmall,free-livingsoilnematodeandhasbeenusedfordevelopmentalbiologyresearchsincethe1960s.•InonesenseitisthebestknownanimalonEarthsincethelocationandlineageofeverycellinembryo,larvaandadultisknown.Drosophila•ThefirstorganismwhosedevelopmentwasunderstoodinmoleculardetailwasthefruitflyDrosophilamelanogaster.Drosophilaishighlysuitedtogeneticexperimentationbecauseofitssmallsizeanditsshortlifecycleof2weeks.Seaurchin•Seaurchinsareoneofthetraditionalmodelorganismsindevelopmentalbiology.Theuseofseaurchinsinthiscontextoriginatesfromthe1800s,whentheembryonicdevelopmentoftheseaurchinswasnoticedtobeparticularlyeasilyviewedbymicroscopy.Seaurchinswerethefirstspeciesinwhichthespermcellswereproventoplayanimportantroleinreproductionbyfertilizingtheovum.Amphioxus•Amphioxus,acephalochordate,haslongbeenregardedastheextantinvertebratemostcloselyrelatedtotheproximateancestorofvertebrates,whichisofgreatsignificancetounderstandoftheoriginandevolutionofvertebrates.Tunicate•Tunicate,alsoknownasurochordata,tunicata(andbythecommonnamesofurochordates,seasquirts,andseapork)isthesubphylumofagroupofunderwatersaclikefilterfeederswithincurrentandexcurrentsiphons,thataremembersofthephylumChordata.Likeotherchordates,tunicateshaveanotochordduringtheirearlydevelopment,butlackmyomericsegmentationthroughoutthebodyandtailasadults.Zebrafish•D.rerioareacommonandusefulmodelorganismforstudiesofvertebratedevelopmentandgenefunction.Theymaysupplementhighervertebratemodels,suchasratsandmice.PioneeringworkofGeorgeStreisingerattheUniversityofOregonestablishedthezebrafishasamodelorganism;itsimportancewasconsolidatedbylargescaleforwardgeneticscreens(commonlyreferredtoastheTübingen/Bostonscreens).Xenopus•Xenopusareapopularmodelsystemforgeneandproteinexpressionandknockdownstudies.TheafricanclawedfrogXenopuslaevishasbeentheworldstandardformanyyears.Thisisbecauseofitseaseofmaintenance,easeofinducedspawning,androbustnessoftheembryos.Xenopustropicalisprovidesasimplermodelforgeneticstudies,havingadiploidgenome.Chick•Thevisiblecourseofdevelopmentofthechickissuperficiallyverydifferentfromthelowervertebratesandismuchclosertothemammaliantype.Becausethechickhasbeenextensivelyusedforworkonlaterstagesofdevelopment,ageneraldescriptionofvertebrateorganogenesisisgivenhere,althoughthistooisfairlysimilarintheothervertebrateclasses.Mouse•Unliketheothermodelorganismsconsideredhere,mammalsareviviparousandtheresultinginaccessibilityofthepostimplantationstagesofdevelopmenthasrepresentedamajorproblemfortheembryologist.Thereforemostdevelopmentalbiologyofthemouseisdonenotbymicrosurgicalmethodsbutbygeneticmanipulation(transgenesisorknockout).HumanThankyou!