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