Download - The Theory of Evolution - CVHS Chicklas
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The Theory of Evolution
MechanismsofEvolution
NotesPt.4
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Population Genetics & Evolution
– IMPORTANTTOREMEMBER:Populations,notindividuals,evolve.
– Population=agroupofindividualsofthesamespecieslivinginaparticularareaatthesametime.
– Allallelesofapopulation’sgenes=itsGENEPOOL.
– Thepercentageofanyonespecificalleleisknownastheallelicfrequency.
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Variations in the Same Species
– Anyvariations(differencesamongmembersofaspecies)withinthesamespecies,likepeoplehavingdifferentheights,arecausedbydifferentallelesinthegenepool.
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Changes in Allelic Frequency
– Iftheallelicfrequencystaysthesameovermanygenerations,itisingeneticequilibrium,andisnotevolving.
– But,changesintheallelicfrequencycanbecausedbymutationsorbychance,knownasgeneticdrift.Thisresultsinevolution.
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Genetics Review
–Genes:segmentsofDNAonachromosome
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Alleles
– Allelesaredifferentversionsofagene
– ex)Theeyecoloralleles:blue,brown,etc
– Individualshave2allelesforeverygene
BlueAllelefromDad
BrownAllelefromMom
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Genotype vs. Phenotype
– Genotype:Anindividualsgeneticmakeup
– Phenotype:Anindividual’sappearance
– Genotypedeterminesphenotype
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Evolution
– Evolution:Achangeinapopulationovertime
–Geneticevolution:Achangeingenefrequencyovertime
– Genefrequency:Whatpercentofanalleleispresentinapopulation
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Mechanisms of Evolution
– Anythingthatchangesthefrequencyofallelesinapopulationisamechanismofevolution
1. NaturalSelection
2. Mutation
3. GeneticDrift
4. GeneFlow(Migration)
5. Non– RandomMating
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1. Natural Selection
– Individualswiththebestadaptedphenotypeswillsurviveandpassontheirgenestothenextgeneration.
– Inthenextgenerationthereshouldbeahigherfrequencyofallelesforthebetteradaptedphenotype
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Natural Selection Example
Generation 1
Mating!
Generation2
GreenAlleleFrequency
2/5=0.4 1/8 =0.125
BrownAlleleFrequency
3/5=0.6 7/8=0.875
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Types of Natural Selection
– Stabilizing:Removesextremes
– Directional:Increasestheoccurrenceofoneextreme
– Disruptive/diversifying:Removesaveragetraits,favorsbothextremes
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Artificial Selection
– Selectivebreedingofdomesticatedplantsandanimalstoproduceoffspringwithdesiredgenetictraits
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2. Mutation
– Amutationinaparent’sDNAcouldresultinoffspringwithdifferentalleles,changingtheallelefrequencyofthepopulation
Generation 1
Mating!
Generation2
GreenAlleleFrequency
2/2=1 2/3 =0.67
BrownAlleleFrequency
0/2=0 1/3=0.33
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3. Gene Flow (Migration)
– Geneflowisanymovementofgenesfromonepopulationtoanother.
– Wind,habitatchange,moving,etc.canallcauseorganismstomigrate,causinggeneflow
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4. Non- Random Mating
– Iforganismscanchoosetheirmatingpartners,thenthemoredesirablealleleswillhaveahigherfrequencyinfuturepopulations
– Thisiscalledsexualselection.Sexualselectioncanresultinsomebizarretraits.
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5. Genetic Drift
– Geneticdriftoccurswhentheallelefrequencyofapopulationchangesbychance.
Generation 1
DIE!
Generation2
GreenAlleleFrequency
3/9=0.33 1/7 =0.14
BrownAlleleFrequency
6/9=0.67 6/7=0.86
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5. Genetic Drift
– Verycommoninsmallpopulations
– FounderEffect:Smallpopulationsettlesanewlocation(oftenislands)
– Bottleneck:Occursafteramajorpopulationdecline(manyendangeredspecies)
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The Evolution of Species
– Speciationistheevolutionofnewspecies.
– Thisoccurswhenaspecies(agroupoforganismsthatcaninterbreedtoproducefertileoffspring)cannolongerinterbreedintheircurrentenvironment.
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Speciation
– Speciationcanoccurwhenpopulationsaresplitapartbygeographicisolation,suchasvolcanoes,fires,sealevelchangesandotherenvironmentalinfluences.
– Eachindividualpopulationadaptstoits“new”environment,eventuallyforminganew,differentspecies.
– REMEMBER:thishappensoverLONGperiodsoftime,likemanygenerations!
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Adaptive radiation
– Thistheorysaysthatonespeciescanmigrate,ormovebytransplantation,tonewhabitatsandchangetofitthatnewenvironment.
– Whenthishappens,severalnewspeciescanarise.
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Adaptive Radiation (Cont)
– Examples:
– TheHawaiianHoneycreeperformed14newspecies.
– Darwin’sFinches
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Divergent Evolution
– Adaptiveradiationcancausedivergentevolution.
– Thisiswhencloselyrelatedorganismsdevelopbodypartsthathavedifferentfunctions,likethebackbonesofsnakesandlizards.
– ThisresultsinalargeamountofBIODIVERSITYallthroughouttheworld!
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Hardy- Weinberg Equilibrium
– Apopulationthatisnotevolvingisconsideredtobein“Hardy- WeinbergEquilibrium”becausetheallelefrequenciesdonotchange.
– Thefollowingsituationsdisrupt“Hardy-WeinbergEquilibrium”andcauseevolution
1. NaturalSelection
2. Mutation
3. GeneticDrift
4. GeneFlow(Migration)
5. Non- RandomMating