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Unit3.4MechanismsofEvolutionNotesOutlineLearningObjectives:• discusspatternsobservedinevolution.• Describefactorsthatinfluencespeciation.• Comparegradualismwithpunctuatedequilibrium.

I. MechanismsofEvolution

• Darwin’stheoryofnaturalselectionremainsthecentralthemeof .• Scientistsoftodayknowthat:

• Evolutionoccursatthe level,with astherawmaterial.

A. PopulationGenetics

1. Hardy-WeinbergPrinciplestatesthatwhenallelicfrequenciesremainconstant,apopulationisingenetic .

a) Eventhoughthenumberofowlsdoubled,the ofgraytoredowlsremainedthesame.

2. p2+2pq+q2=1

a) Thisequationallowustodeterminethe ofeach inthepopulation.

(1) homozygousdominant:

(2) heterozygous:

(3) homozygousrecessive:

(4) Note:thesumofthesefrequenciesequals .

3. Apopulationingeneticequilibriummustmeetall ofthefollowingconditions:

a) Thepopulationisvery

b) No or

c) Matingis

d) donotoccur(nonewvariations)

e) doesnotoccur

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B. GeneticDriftisachangeintheallelicfrequenciesinapopulationthatis:

In populationstheeffectsofgeneticdriftbecomemorepronounced,andthechanceoflosingan becomesgreater.

1. FounderEffectoccurswhenasmallsampleofapopulationsettlesinalocation fromtherestofthe .

a) allelesthatwere intheoriginalpopulationmightbe inthenewpopulation.

2. Bottleneckoccurswhenapopulation toaverylownumberandthen .

a) Can genetic

C. GeneFlow

1. Nonewgenes thepopulationandnogenes thepopulation.

2. Apopulationin experiencesnogeneflow,however,fewpopulationsare .

3. movementofindividualsbetweenpopulations differencesbetweenpopulations.

D. NonrandomMating

1. Rarelyismatingcompletely inapopulation.

2. Usuallyindividualsmatewithindividualsinclose .

3. Thispromotesinbreedingandcouldleadtoachangeinallelicproportionsfavoringindividualsthatare forparticulartraits.

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E. Mutation

1. Amutationisa ingeneticmaterial

2. Occasionallymutationsprovidean toorganismsandbecomemore insubsequentgenerations.

3. Basisuponwhich works.

F. NaturalSelection

Selecttheindividualsthatarebestadaptedfor and .

1. Selection—eliminateextremeexpressions

a)

2. Selection—increasestheexpressionoftheextremeversionofatrait

a)

3. Selection—splitsapopulationintotwogroups

a) —brownskinifliveingrassyarea,greyskinifliveonrockyislandshore.

4. Selectionoperatesinpopulationswheremalesandfemalesdiffersignificantlyinappearance.

a) malesare and inthegroup

b) morelikely yetbodiesarestillenhancedforreproductivesuccess

(1) Examples:

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II. ReproductiveIsolation

A. PrezygoticIsolation:

1. EasternandWesternmeadowlarksaresimilarinappearancebuttheirmatingsongsseparatethem .

B. PostzygoticIsolation—occurswhen butahybridoffspringcannot or .

1. Aligeristheoffspringofamalelionandafemaletiger.Ligersare .

III. SpeciationForspeciationtooccur,apopulationmust andthenbereproductively .

A. AllopatricSpeciation:a barrierdividesonepopulationintotwoormorepopulations.

1. example—squirrelsintheGrandCanyon

B. SympatricSpeciation:speciesevolveintoanewspecies aphysicalbarrier

1. example—applemaggotflieslayeggsonapplesorhawthornsdependingonthetypeoffruittheygrewupon.

IV. PatternsofEvolution

A. AdaptiveRadiation—akaDivergentEvolution

1. Canoccurinarelatively timewhen speciesgivesriseto differentspeciesinresponsetothecreationof orsomeotherecologicalopportunity.

a) followslargescale events

b) CichlidfishofLakeVictoriainAfrica

B. Coevolution

1. Therelationshipbetweentwospeciesmightbesoclosethat:

a) —occurswhentwospeciesbenefiteachother.

b) cometorchidsandmothsthatpollinatethem.

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2. Coevolutionaryarmsrace—onespeciescanevolvea dependencyonanotherspecies.

a) aplantandaninsectthatisdependentontheplantforfood

(1) theplantevolvesa defense

(2) Theinsectsevolvethe toresistthedefense.

(3) Theresponsecontinuestoescalate

C. ConvergentEvolution

1. speciesevolvesimilartraitseventhoughtheylive:

2. Occursinenvironmentsthataregeographicallyfarapartbuthavesimilar:

D. RateofSpeciation

1. PunctuatedEquilibrium—explains spurtsofgeneticchangecausingspeciestodiverge .Theseperiodspunctuatemuchlongerperiodswhenthespeciesexhibitlittlechange.

2. Gradualism—evolutionproceedsin , steps