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CH.16.1–GenesandVariation HowCommonIsGeneticVariation? VariationandGenePools Geneticvariationisstudiedin_______________________orgroupof individualsofthesamespeciesthatinterbreed. A___________________________consistsofallgenes,includingallthedifferent alleles,thatarepresentinapopulation. Therelativefrequencyofanalleleisthe___________________________________ ______________________inagenepool,comparedwiththe_____________ ______________________________(usuallyexpressedasapercent). Howisevolutiondefinedingeneticterms? Ingeneticterms,evolutionis___________________________intherelative frequencyofallelesinapopulation. Whatarethemainsourcesofheritablevariationinapopulation? SourcesofGeneticVariation Thetwomainsourcesofgeneticvariationare________________________ andthe_________________________thatresultsfromsexualreproduction. Mutations Amutationis___________________________inasequenceofDNA. Mutationsoccurbecauseof_____________________inDNA____________________ orasaresultofradiationorchemicalsintheenvironment. Mutations___________________alwaysaffectthewayanorganismlooks,or itsphenotype. GeneShuffling Mostheritabledifferencesaredueto___________________________. Crossing-over,whichoccursduringmeiosis,_____________________the numberofgenotypesthatcanappearinoffspring. Sexualreproductionproduces______________________phenotypes,butit doesnotchangetheamountofallelesinapopulation. 16-2EvolutionasGeneticChange Naturalselectionaffectswhichindividuals________________________and ______________________and___________________________. Ifanindividualdieswithoutreproducing,it_______________________ contributeits_______________________tothepopulation’s____________________. Ifanindividualproduces_____________________________,its____________________ ___________________________andmayincreasein_________________________. Evolutionisanychangeovertimeintherelativefrequenciesofallelesin apopulation. _______________________,notindividualorganisms,can________________________ __________________. NaturalSelectiononSingle-GeneTraits Howdoesnaturalselectionaffectsingle-genetraits? Naturalselectiononsingle-genetraitscanleadto_____________________ ________________________andthusto____________________. Organismsofonecolormayproducefeweroffspringthanorganismsof othercolors. Forexample,alizardpopulationisnormally__________________,buthas ________________________thatproduce____________and_______________forms. Redlizardsaremorevisibletopredators,sotheywill____________________ ____________________________________.Therefore,thealleleforredcolorwill become________________. Blacklizardsmaywarmupfasteroncolddays.Thismaygivethem energyto_______________________________________.Inturn,theymayproduce _________________________________. Thealleleforblackcolorwill________________________________________________. NaturalSelectiononPolygenicTraits Howdoesnaturalselectionaffectpolygenictraits? Naturalselectioncanaffectthedistributionsofphenotypesinany ofthreeways: •___________________________selection •___________________________selection •disruptiveselection DirectionalSelection Whenindividualsatoneendofthepopulationcurvehave________________ _______________________thanindividualsinthemiddleorattheotherend, directionalselectiontakesplace. Therangeofphysicalcharacteristics,________________________,shiftsas someindividualssurviveandreproducewhileothersdonot. Inthiscase,birdswithlargerbeakshave__________________________. Therefore,theaveragebeaksize______________________. Drawgraphbelow… StabilizingSelection Whenindividualsnearthe_________________________________havehigher fitnessthanindividualsateitherendofthecurve,stabilizingselection takesplace. Thiskeepsthecenterofthecurveatits________________________________,but itnarrowstheoverallgraph. Humanbabiesbornatanaveragemassaremorelikelytosurvivethan babiesborneithermuchsmallerormuchlargerthanaverage. Drawgraphbelow… DisruptiveSelection Whenindividualsatthe____________________and_____________________ends ofthecurvehavehigherfitnessthanindividualsnearthemiddle, disruptiveselectiontakesplace. Ifthepressureofnaturalselectionis__________________enoughand ____________________enough,thecurvewill______________,creatingtwo distinctphenotypes. Ifaverage-sizedseedsbecomescarce,abirdpopulationwillsplitinto twogroups:onethateatssmallseedsandonethateatslargeseeds. Drawgraphbelow… 16.2cont… GeneticDrift Whatisgeneticdrift? A__________________________________in_______________________________________is calledgeneticdrift. In_________________populations,individualsthatcarryaparticular allele,orcharacteristic,mayleavemoredescendantsthanother individualsdo,just_____________________________. _______________________,aseriesofchanceoccurrencesofthistypecan causean_____________________tobecome_________________inapopulation. Geneticdriftmayoccurwhena________________________ofindividuals colonizesa_______________habitat. Thoseindividualsmaycarry_________________ofa___________________________ thanthelargerpopulationhad. Thenewpopulationwillbe________________________________________________ fromthe________________________population. Whenallelefrequencieschange________________________________ofasmall subgroupofapopulationitisknownasthe_______________________________. EX.Largerpopulationismadeupof… FoundingpopulationAismadeupof… FoundingpopulationBismadeupof… DescendantsofpopulationAaremadeupof… DescendantsofpopulationBaremadeupof… EvolutionVersusGeneticEquilibrium TheHardy-Weinbergprinciplestatesthat_________________frequencies inapopulationwillremain_________________unlessoneormorefactors causethosefrequenciesto_______________. Whenallelefrequenciesremainconstantitiscalledgenetic equilibrium. Whatfiveconditionsareneededtomaintaingeneticequilibrium? _______________conditionsarerequiredtomaintaingenetic _____________________________fromgenerationtogeneration: •theremustbe_____________________mating, •thepopulationmustbevery__________________, •therecanbe______________________________intooroutofthepopulation, •therecanbe______________________________,and •therecanbe________________________________________. RandomMating Randommatingensuresthat____________________________hasan____________ ________________________ofpassingonitsallelestooffspring. Doesthishappeninnature? Arematesselectedduetosomedesirablecharacteristic? LargePopulation Smallpopulations_____________________reachgeneticequilibriumeasily duetogeneticdrifthavinga________________________onasmallpopulation. Allelefrequenciesoflargepopulationsare_______________________tobe changedthroughtheprocessofgeneticdrift. NoMovementIntoorOutofthePopulation Becauseindividualsmaybring_____________________intoapopulation, theremustbe___________________________________intooroutofapopulation. Thepopulation'sgenepoolmustbekept_______________________andkept ______________________fromthegenepoolsofotherpopulations. NoMutations Ifgenesmutate,________________________maybeintroducedintothe population,andallelefrequencies____________________________. NoNaturalSelection _______________________inthepopulationmusthave_______________ probabilitiesof______________________and________________________. _______________________________canhaveaselectiveadvantageoveranother. Therecanbe__________________________________operatingonthepopulation. 16-3TheProcessofSpeciation Naturalselectionandchanceeventscan____________________________________ _____________________________________inapopulationandleadtospeciation. Speciationistheformationof_______________________. Aspeciesisagroupoforganismsthat__________________withoneanother andproduce__________________________________________. Thegenepoolsoftwopopulationsmustbecome__________________________ forthemtobecomenewspecies. IsolatingMechanisms Asnewspeciesevolve,populationsbecomereproductivelyisolated fromeachother. Whenthemembersoftwopopulations_____________________________________ andproducefertileoffspring,reproductiveisolationhasoccurred. Reproductiveisolationcandevelopinavarietyofways,including: •___________________________isolation •___________________________isolation •___________________________isolation BehavioralIsolation Behavioralisolationoccurswhentwopopulationsarecapableof breedingwithoneanotherbuthave_________________________________________ orotherreproductivestrategiesthatinvolvebehavior. GeographicIsolation Geographicisolationoccurswhentwopopulationsareseparatedby geographicbarrierssuchas___________________or___________________________. Geographicbarriers_____________guaranteethecreationofanewspecies. TemporalIsolation Temporalisolationoccurswhentwoormorespecies___________________ _________________________________. SpeciationinDarwin'sFinches SpeciationintheGalápagosfinchesoccurredby: •_________________________ofanewpopulation •geographic__________________________ •changesinnewpopulation's________________________ •___________________________isolation •ecological_________________________ FoundersArrive SpeciesAcomesfrom____________________________totheGalapagos, _______________________and_________________________ GeographicIsolation SpeciesAtravelsto_________________________andcreatesanew ___________________________. ChangesintheGenePool ________________________onthesecondislandfavorbirdswith _________________beaks. Pop.Bappearson_______________________with____________________________. ReproductiveIsolation IfpopulationBbirdscrossbacktothefirstisland,they__________________ ___________________withbirdsfrompopulationA. PopulationsAandBare____________________________. EcologicalCompetition AsspeciesAandBcompeteforavailableseedsonthefirstisland,they continueto______________________inawaythatincreasesthedifferences betweenthem. A______________________________—C—___________________________. ContinuedEvolution Thisprocessofisolation,geneticchange,andreproductiveisolation probablyrepeateditselfoftenacrosstheentireGalápagosislandchain. Chapter17Notes Section17.4PatternsofEvolution Whatisadaptiveradiation? Drawadiagramofadaptiveradiation. Whatisconvergentevolution? Giveanexampleofconvergentevolution. Whatiscoevolution? Giveanexampleofcoevolution.
