evolution of populations - Weeblykylecollinsbiology.weebly.com/.../evolution_of_populations.pdf ·...
Transcript of evolution of populations - Weeblykylecollinsbiology.weebly.com/.../evolution_of_populations.pdf ·...
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EvolutionofPopulations
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• GenePools1. Allofthegenesinapopulation
- Contains2ormorealleles(formsofagene)foreachtrait
2.Relativefrequencies- #oftimesanalleleoccursinagenepoolcomparedtootheralleles
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• SourcesofGeneticVariation1. Mutations
- Causes=mistakesinreplication,radiationorchemicals- Mayormaynoteffectphenotype
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2. GeneShuffling– Occursduringproductionofgametes- 8.4million(2^23)differentcombinationsofgenes
- Crossingoveralsoincreasesgenotypes
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• SingleGeneandPolygenicTraits1. #ofphenotypesproducedforagiventrait
dependsonthenumberofgenesthatcontrolthetrait
- Single-genetrait– controlledbyasinglegenethathas2alleles
- Hasfewerphenotypesthanapolygenictrait- Show’ssimpledominant-recessivepattern–
Widow’sPeak
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2. PolygenicTraits– Controlledby2ormoregenes[height]
- Showawiderangeofphenotypes
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16-2EvolutionasGeneticChange
• NaturalSelectiononSingle-genetraits1. Canleadtochangesinallelefrequencies&
thustoevolution2. Whitemothvrs.Darkmoth- Frequencyofnewallelewillincreaseifthis
mutationmakessomeindividualsmorefitfortheirenvironment
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• NaturalSelectiononPolygenicTraits1.DirectionalSelection– Whenindividualsatonlyoneendofabellcurveofphenotypefrequencieshavehigherfitnessthanindividualsinthemiddleorattheotherend.
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DirectionalSelectionGraphs
- Evolutioncausesanincreaseinthe#ofindividualswiththetraitatoneendofthecurve
- Example:IncreaseofbeaksizeoffinchesontheGalapagos
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2. StabilizingSelection– Individualswithanaverageformofatrait(nearcenterofcurve)havehighestfitness
- Keepscurveatitscurrentposition- Example:birthweight
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3. DisruptiveSelection– individualsatbothendsofthecurvehavehigherfitnessthanindividualsnearthecenter
- Selectionactsagainstintermediatetype- Cancause2distinctphenotypes- Fincheswithlargeorsmallbeaks
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TestPrepQuestions
• NaturalSelectionactsdirectlyona. Genesb. Mutationsc. Allelesd. genotypes
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TestPrepQuestions
AccordingtotheHardy-Weinbergprinciple,geneticequilibriumwouldbemorelikelyinapopulationif
a. Thepopulationsizerapidlydecreasesb. Mutationratesarehighc. Nonaturalselectiontakesplaced. Thereisfrequentmovementoutofthe
population
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Thegraphbelowisanexampleof
a. Disruptiveselectionb. Geneticdriftc. StabilizingSelectiond. DirectionalSelection
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Thegraphbelowisanexampleof
a. DirectionalSelectionb. StabilizingSelectionc. GeneticDriftd. GenePool
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What’sThis?
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• EvolutionVersusGeneticEquilibrium- Hardy-WeinbergPrinciple:Allelefrequenciesinapopulationwillremainconstantunlessoneormorefactorscausethemtochange.
- GeneticEquilibrium:Situationinwhichallelefreq.ofapop.donotchangeovertime.
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ProcessofSpeciation
• IsolatingMechanisms– Asnewspeciesevolve,populationsbecomereproductivelyisolatedfromeachother
- ReproductiveIsolation– Membersoftwopopulationscannotinterbreed&producefertileoffspring
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a.BehavioralIsolation:Differencesinbehaviorpreventbreeding.
- Example:Easternandwesternmeadowlarks(pg.404)
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b. GeographicIsolation:Separationofpopulationsbybarrierssuchasrivers,mountains,canyons,etc.
c. TemporalIsolation:2ormorespeciesreproduceatdifferenttimes.
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• TestingNaturalSelectioninNature(Peter&RosemaryGrant,Darwin’sFinches)
a. Variation– recordedlotsofvariationontraitsoffinches
b. NaturalSelection– big-beakedbirdssurvivedduringtimesoffoodscarcity
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c. RapidEvolution– Changeinthephenotypesofthefincheschangedquicklyovertime,dependingonthefoodsupply.
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• SpeciationofDarwin’sFinchesa. Arrivalofthefounding populationfrom
SouthAmericab. Separationofpopulations – islandtoislandc. ChangesintheGenePool– bynatural
selection
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d. ReproductiveIsolation– Birdspickedmateswithsimilarsizedbeaks
e. Ecologicalcompetition– forfoodduringdifferentseasons
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f. ContinuedEvolution – 13speciesoffinchesexisttoday
- Exampleof:adaptiveRadiation,theprocessbywhichonespeciesevolvesintoseveraldifferentformsthatliveindifferentways.
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• GeneticDrift:Allelefrequencieschangebecauseofchance.
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• Thecombinedgeneticinformationofallmembersofapopulationformsa
a. Nicheb. Phenotypec. Genepoold. species
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Asinglespeciesthathasevolvedintomanydifferentforms(i.e.Darwin’sFinches)hasundergone
a. PunctuatedEquilibriumb. MassExtinctionc. AdaptiveRadiationd. DirectionalSelection
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Onefactorwhichisnecessaryfortheformationofanewspeciesis
a. Geographicbarriersb. Reproductiveisolationc. Differentmatingbehaviorsd. Temporalisolation
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Similarorganismsthatcanbreedwitheachotherandproducefertileoffspringmakeupa
a. Speciesb. Genepoolc. Populationd. Clone
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Theseparationofpopulationsthatoccursduetotimingofreproductiveactivityiscalled
a. Geographicisolationb. Behavioralisolationc. Temporalisolationd. Geneticdrift
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Geneticdriftinvolveschangesinapopulationdueto
a. Naturalselectionb. Geneticequilibriumc. Chanced. mutations
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Chapter17 TheHistoryofLife• 17-1TheFossilRecord- TheFossilRecordprovidesevidenceofthehistoryoflifeonearthandshowshoworganismshavechangedovertime
- Morethan99%ofallspeciesonearthhavebecomeextinct.
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• Mostfossilsforminsedimentaryrock(pg.418)• Sedimentaryrockformsfromparticlesofsand,silt,andclay.
• Thisprocesspreservestheremainsoforganisms,formingfossils
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• Thefirstorganismsonearthweremostlikelytoday’sbacteria.
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• Coevolution:theprocessbywhich2speciesevolveinresponsetoeachother
- Example:aflowerandapollinatinginsect
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• Massextinctionhasencouragedtherapidevolutionofsurvivingspeciesbymakingnewhabitatsavailabletothem.
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• Hox genes– determineplacementofarms,legs,wings…
- Couldhaveaffectedevolutionthroughsmallchangesintimingduringembryonicdevelopment
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TestPrepQuestions
• 5conditionsforGeneticEquilibrium:
1. RandomMating2. Largepopulation3. Nomovementintooroutofpopulation4. Nomutations5. Nonaturalselection