Part#1:Whatisevolu2on?

Chapters15&16inMiller&Levine�sBiology

Unit #10: Evolution GENEPOOL•  Allofthegenes,andtheirallelesinapopula2on.ALLELEFREQUENCY•  Thenumberof2mesthealleleoccursinagenepoolcompared

tothetotalnumberofallelesinthegenepool.

Numberofpar2cularallelestotal#ofallallelesinthegenepoolx100%=AlleleFrequency

WhatisthefrequencyoftheAallele?

Whatisthefrequencyofthetheaallele?

DONOW:GenePool&AlleleFrequency

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What is evolution? •  Biologicalevolu2onisNOT

simplya�changeover2me.�

•  Therearelotsofthingsinnaturethatchangeover2me:treeslosetheirleaves,mountainrangesriseanderode,etc.TheseexamplesdoNOTinvolvedescentthroughgene2cinheritance.

•  InGENETICterms,evoluHonisanychangeintherelaHvefrequencyofallelesinagenepool.

Part#2:EvidenceofEvolu2on

Chapters15&16inMiller&Levine�sBiology

Darwinfoundconvincingevidenceforhisideasintheresultsofar2ficialselec2on.

ArHficialselecHonistheselec2vebreedingofdomes2catedplantsandanimals.Byselec2ngindividualswiththedesiredtraitsasbreedingstock,humanswereplayingtheroleoftheenvironmentandbringingaboutdifferen2alreproduc2on.Theywere,infact,modifyingspecies.

Darwinfoundevidenceforevolu2oninthefossilrecord.

•  Fossils=theimprintsorremainsoforganismsthatlivedinthepast

•  Sedimentaryrocklayersarecalledstrata.Youngerstrataareontopofolderones;thus,therela2veagesoffossilscanbedeterminedbythelayersinwhichtheyarefound.

•  Thefossilrecordtes2fiesthatorganismshaveevolvedinahistoricalsequence.Theoldestknownfossils,da2ngfromabout3.5billionyearsago,areprokaryotes.

Thereisevidenceforevolu2oninCompara2veAnatomy.

•  HomologousstructuresarefeaturesthatoZenhavedifferentfunc2onsbutarestructurallysimilarbecauseofcommonancestry.Asanexample,thesameskeletalelementsmakeuptheforelimbsofhumans,cats,whales,andbats,buttheirfunc2onsdiffer.

•  Someofthemostinteres2ng

homologousstructuresarevesHgialorgans,structuresofli[le,ifany,importancetotheorganism.Ves2gialorgansareremnantsofstructuresthatservedimportantfunc2onsintheorganism�sancestors.Thesmallhind-legandfootbonesofmodernwhalesareexamples.

Thereisevidenceforevolu2oninCompara2veEmbryology.

Canyoutellthedifferencebetweentheseearlyembryos?

Whatorganismsarethey?

Thereisevidenceforevolu2oninMolecularBiology.

•  Iftwospecieshavegeneswithsequencesthatmatchclosely,biologistsconcludethatthesesequencesmusthavebeeninheritedfromarela2velyrecentcommonancestor.

•  Incontrast,thegreaterthenumberofsequencedifferencesbetweenspecies,thelesslikelytheyshareaclosecommonancestor.

Part#3:MechanismsofEvolu2on

Whatprocessescauseevolu2ontooccur?

Galapagos Finch Evolution

The“FiveFingers”ofEvoluHon

Small Population (Genetic Drift)

Non-Random Mating (Selective Breeding)

Mutations

Gene Flow

Natural Selection (lead to adaptations)

TED-Ed:FiveFingersofEvolu2on(5min)

Besidesnaturalselec2on,therearemechanismsofevolu2oninnature:

MutaHonAmuta2oncouldcauseparentswithgenesforbrightgreencolora2ontohaveoffspringwithageneforbrowncolora2on.Thatwouldmakethegenesforbrownbeetlesmorefrequentinthepopula2on.

MigraHon(GeneFlow)Someindividualsfromapopula2onofbrownbeetlesmighthavejoinedapopula2onofgreenbeetles.Thatwouldmakethegenesforbrownbeetlesmorefrequentinthegreenbeetlepopula2on.

GeneHcDriZImaginethatinonegenera2on,twobrownbeetleshappenedtohavefouroffspringsurvivetoreproduce.Severalgreenbeetleswerekilledwhensomeonesteppedonthemandhadnooffspring.Thenextgenera2onwouldhaveafewmorebrownbeetlesthanthepreviousgenera2on-butjustbychance.Thesechancechangesfromgenera2ontogenera2onareknownasgene2cdriZ.

Non-RandomMaHngisalsocalledAr2ficialSelec2onArHficialSelecHon(orSelecHveBreeding)Whenindividualschoosetheirmatebasedonasingulartraitratherthanthroughsexualselec2on,thenthenextgenera2onwillseeanincreaseinallelicfrequencyforcertaintraits.Forexample,ifbeetlesallbeganma2ngbrowntobrownsimplybecausetherewereveryfewgreenbeetlesintheirloca2on,thenfuturegenera2onsofbeetleswouldhavemorebrownbeetles.

Forexample,farmershavecul2vatednumerouspopularcropsfromthewildmustard.

Charles Darwin’s theory of NATURAL SELECTION: Nature favors the survival and reproduction of organisms that are best-

suited for the environment.

1.ThereisgeneHcvariaHonintraits.Forexample,somebeetlesaregreenandsomearebrown.

2.ThereisdifferenHalreproducHon.Sincetheenvironmentcan�tsupportunlimitedpopula2ongrowth,notallindividualsgettoreproducetotheirfullpoten2al.Inthisexample,greenbeetlestendtogeteatenbybirdsandsurvivetoreproducelessoZenthanbrownbeetlesdo.

3.Thereisheredity.Thesurvivingbrownbeetleshavebrownbabybeetlesbecausethistraithasagene2cbasis.

4.Endresult:Themoreadvantageoustrait,browncolora2on,whichallowsthebeetletohavemoreoffspring,becomesmorecommoninthepopula2on.Ifthisprocesscon2nues,eventually,allindividualsinthepopula2onwillbebrown.

Charles Darwin’s theory of NATURAL SELECTION: Nature favors the survival and reproduction of organisms that are best-

suited for the environment.

1. The struggle for existence 2. Variation and Adaption

3. Survival of the Fittest 4. Natural Selection

Threedifferenteffectsofnaturalselec2ononapolygenictraitwithinapopula2on.

Rocket Pocket Mice VIDEO: https://youtu.be/sjeSEngKGrg

TheHardy-WeinbergPrinciple•  Allelefrequenciesinapopula2onwillremainconstantunlessoneormorefactorscausethosefrequenciestochange.Thesitua2oninwhichallelefrequenciesremainconstantiscalledgeneHcequilibrium.

•  Fivecondi2onsarerequiredtomaintaingene2cequilibrium:–  TheremustberandommaHng.–  Thepopula2onmustbeverylarge.–  TherecanbenomigraHon.–  TherecanbenomutaHons.–  TherecanbenonaturalselecHon.

Natural Selection produces ADAPTATIONS in organisms. An adaptation is a feature that is common in a population because it provides some improved function. Adaptations are well fitted to their function. Adaptations take on many forms. For example: Mimicry of leaves by insects such as the katydid from Costa Rica is great for evading its predators. The creosote bush is a desert-dwelling plant that produces toxins that prevent other plants from growing nearby, thus reducing competition for nutrients and water. Echolocation in bats is an adaptations for catching insects.

Part#4:Misconcep2ons

Willallorganismsbeabletoevolvetohaveadapta2onstosuittheirchangingenvironment?Willnaturalselec2onevermaketheperfect

organismwithenough2me?

Jean-Baptiste Lamarck proposed that organisms do acquire certain characteristics during their lifetime because of an innate desire or need to be better suited to survive in

their environment. This is INCORRECT.

Part#5:Specia2on

Macroevolu2on

Hownewspeciesarise•  SpeciaHon-aneventthatproducestwoormoreseparate

species.•  Species-agroupofindividualsthatinterbreedinnature

andproducefer2leoffspring.

Forexample,thesehappyfacespiderslookdifferent,butsincetheycaninterbreed,theyareconsideredthesamespecies:Theridiongrallator.

Specia2onEvents

•  Imaginethatyouarelookingata2pofthetreeoflife.Eachbranchingpointisaspecia2onevent.Atthatpointgene2cchangesresultedintwoseparatespecieswherepreviouslytherehadjustbeenone.

•  Butwhyandhowdidithappen?

Reproduc2veIsola2on

1.  GeographicIsola2on2.  HabitatIsola2on3.  TemporalIsola2on4.  BehavioralIsola2on5.  MechanicalIsola2on6.  Game2cIsola2on

Inorderforspecia2ontooccur,twopopula2onsneedtobereproduc2velyisolatedforaperiod2metoallowforsignificantgene2cchangesintheirgenepool.Thismaybedoneinanumberofways:

GeographicIsola2on•  Twospeciesthatoccupydifferentgeographicareasduetoaphysicalbarrier,suchaswaterwaysormountainranges.

HabitatIsola2on•  Twospeciesthatoccupydifferenthabitatswithinthesameareamayencountereachotherrarely,ifatall,eventhoughtheyarenotisolatedbyobviousphysicalbarriers.

•  Example:Twospeciesofgartersnakesliveinthesamegeographicarea,butonelivesmainlyinwaterwhiletheotherisprimarilyterrestrial.

TemporalIsola2on•  Speciesthatbreedduring

different2mesoftheday,differentseasons,ordifferentyearscannotmixtheirgametes.

•  Example:InNorthAmerica,thegeographicrangesofthewesternspo[edskunkandtheeasternspo[edskunkoverlap,butonematesinthelatesummerandthematesinthelatewinter.

BehavioralIsola2on•  Courtshipritualsthata[ractmatesandotherbehaviorsuniquetoa

speciesareeffec2vereproduc2vebarriers,evenbetweencloselyrelatedspecies.Suchbehaviorritualsenablematerecogni2on–awaytoiden2fypoten2almatesofthesamespecies.

•  Example:Blue-footedboobiesmateonlyaZeracourtshipdisplayuniquetotheirspecies.Partofthe“script”callsforthemaletohigh-step,abehaviorthatcallsthefemale’sa[en2ontohisbrightbluefeet.

MechanicalIsola2on•  Ma2ngisa[empted,butmorphologicaldifferencesprevent

itssuccessfulcomple2on.•  Example:Theshellsoftwospeciesofsnailsspiralindifferent

direc2ons:Movinginwardtothecenter,onespiralsinacounterclockwisedirec2on,theotherinaclockwisedirec2on.Asaresult,thesnails’genitalopeningsarenotaligned,andma2ngcannotbecompleted.

Game2cIsola2on•  Spermofonespeciesmaynotbeabletofer2lize

theeggsofanotherspecies.Forinstance,spermmaynotbeabletosurviveinthereproduc2vetractoffemalesoftheotherspecies,orbiochemicalmechanismsmaypreventthespermfrompenetra2ngthemembranesurroundingtheotherspecies’eggs.

•  Example:Game2cisola2onseparatescertaincloselyrelatedspeciesofaqua2canimals,suchasseaurchins.Seaurchinsreleasetheirspermandeggsintothesurroundingwater,wheretheyfuseandformzygotes.Itisdifficultforgametesofdifferentspecies,suchastheredandpurpleurchinsshownhere,tofusebecauseproteinsonthesurfacesoftheeggsandspermbindverypoorlytoeachother.