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