gene pool unit #10: evolution
TRANSCRIPT
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Part#1:Whatisevolu2on?
Chapters15&16inMiller&Levine�sBiology
Unit #10: Evolution GENEPOOL• Allofthegenes,andtheirallelesinapopula2on.ALLELEFREQUENCY• Thenumberof2mesthealleleoccursinagenepoolcompared
tothetotalnumberofallelesinthegenepool.
Numberofpar2cularallelestotal#ofallallelesinthegenepoolx100%=AlleleFrequency
WhatisthefrequencyoftheAallele?
Whatisthefrequencyofthetheaallele?
DONOW:GenePool&AlleleFrequency
A A
A A
A A
A A
A a A a
A a
a a
What is evolution? • Biologicalevolu2onisNOT
simplya�changeover2me.�
• Therearelotsofthingsinnaturethatchangeover2me:treeslosetheirleaves,mountainrangesriseanderode,etc.TheseexamplesdoNOTinvolvedescentthroughgene2cinheritance.
• InGENETICterms,evoluHonisanychangeintherelaHvefrequencyofallelesinagenepool.
Part#2:EvidenceofEvolu2on
Chapters15&16inMiller&Levine�sBiology
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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?
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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.
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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
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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.
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Part#5:Specia2on
Macroevolu2on
Hownewspeciesarise• SpeciaHon-aneventthatproducestwoormoreseparate
species.• Species-agroupofindividualsthatinterbreedinnature
andproducefer2leoffspring.
Forexample,thesehappyfacespiderslookdifferent,butsincetheycaninterbreed,theyareconsideredthesamespecies:Theridiongrallator.
Specia2onEvents
• Imaginethatyouarelookingata2pofthetreeoflife.Eachbranchingpointisaspecia2onevent.Atthatpointgene2cchangesresultedintwoseparatespecieswherepreviouslytherehadjustbeenone.
• Butwhyandhowdidithappen?
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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.
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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.