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The Making of the Fittest: Natural Selection and Adaptation
Lesson The Making of the Fittest Natural Selection and Adaptation Educator Materials
PublishedFebruary,2017
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INTRODUCTIONTOTHEMOLECULARGENETICSOFTHECOLORMUTATIONSINROCKPOCKETMICE
OVERVIEWTheselessonsserveasanextensiontotheHowardHughesMedicalInstituteshortfilmTheMakingoftheFittest:NaturalSelectionandAdaptation.Studentswilltranscribeandtranslateportionsofthewild-typeandmutantrockpocketmouseMc1rgene.BycomparingDNAsequences,studentsidentifythelocationsandtypesofmutationsresponsibleforthecoat-colorchangedescribedinthefilm.StudentswillansweraseriesofquestionstoexplainhowachangeinaminoacidsequenceaffectsthefunctionalityoftheMC1Rprotein,andhowthatchangemightdirectlyaffectthecoatcoloroftherockpocketmousepopulationsandthesurvivalofthatpopulation.KEYCONCEPTSANDLEARNINGOBJECTIVES
• Amutationisarandomchangetoanorganism’sDNAsequence.• Mostmutationshavenoeffectontraits,butsomemutationsaffecttheexpressionofageneand/orthe
geneproduct.• Theenvironmentcontributestodeterminingwhetheramutationisadvantageous,deleterious,orneutral.• Naturalselectionpreservesfavorabletraits.• Variation,selection,andtimefueltheprocessofevolution.• Boththetypeofthemutationanditslocationdeterminewhetherornotitwillhaveaneffecton
phenotype(advancedversiononly).Studentswillbeableto:
• transcribeandtranslateaDNAsequence.• connectDNAchangestophenotype.• analyzeandorganizedata.
CURRICULUMCONNECTIONSCurriculum StandardsNGSS(April2013) HS-LS1-1,HS-LS3-1,HS-LS3-2,HS-LS4-2,HS-LS4-4,HS-LS4-5
HS.LS1.A,HS.LS4.B,HS.LS4.CCommonCore(2010) CCSS.ELA-Literacy.RST.9-10.3,CCSS.ELA-Literacy.RST.9-10.4,
CCSS.ELA-Literacy.RST.9-10.7APBiology(2012–13) 1.A.1,1.A.2,3.A.1,3.C.1,4.B.1IBBiology(2009) 3.5,4.1,4.3,5.4,7.3,7.4,D.2,G.1
KEYTERMSevolution,naturalselection,variation,trait,mutation,adaptationTIMEREQUIREMENTTheseactivitiesaredesignedforone50-minuteclassperiodincludingshowingthefilm.Additionaltimefortheanalysisquestionsmightberequiredforhomeworkdependingonstudents’pace.Bothactivitiescoverthesamematerial,butactivity2hasadditionalmaterialcoveringintracellular,transmembrane,andextracellulardomains.
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Lesson The Making of the Fittest Natural Selection and Adaptation
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SUGGESTEDAUDIENCEActivity1:Theactivityisdesignedforhighschoolbiology(primarilyfirst-yearbiology,bothregularandhonors).Activity2:TheactivityisdesignedforAPandIBhighschoolbiologyandintroductorycollegebiology.PRIORKNOWLEDGEStudentsshouldbefamiliarwiththedefinitionsof“gene”and“protein.”Theyshouldalsobecomfortablewithbasicmoleculargenetics,includingafamiliaritywiththeprocessesoftranscriptionandtranslation.Finally,studentsshouldunderstandthataprotein’saminoacidsequencedeterminesitsstructure,whichdeterminesitsfunction.MATERIALSStudentswillneed:geneticcodechart(providedinstudentmaterials)blue,red,andgreencoloredpencilsTEACHINGTIPS
• Ifyoudonothaveaccesstoacolorprintertoprintthechartonpage2ofthisdocument,youshouldcomparestudents’worktohowthechartsbelowappearonyourcomputerscreen.
• Youcouldassignanalysisquestionsashomeworktoreducetheamountofclasstimerequiredforthislesson.
ANSWERKEYACTIVITY1GENETABLE1:WILD-TYPEMC1RGENE(LIGHTCOAT-COLORPHENOTYPE)
015 022DNA TTG AGG TGG GCG TGT CCG CAA GGAmRNA AAC UCC ACC CGC ACA GGC GUU CCUAminoAcid Asn Ser Thr Arg Thr Gly Val Pro
105 112
DNA CGG GAC CGG TGG GCC CAC TGA CACmRNA GCC CUG GCC ACC CGG GUG ACU GUGAminoAcid Ala Leu Ala Thr Arg Val Thr Val
154 161
DNA TCA TAA CAC TGT GAC GGG GCC CGAmRNA AGU AUU GUG ACA CUG CCC CGG GCUAminoAcid Ser Ile Val Thr Leu Pro Arg Ala
209 212
DNA GTG TAC GAA CGTmRNA CAC AUG CUU GCAAminoAcid His Met Leu Ala
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The Making of the Fittest: Natural Selection and Adaptation Educator Materials
Lesson The Making of the Fittest Natural Selection and Adaptation
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230 237
DNA GAA CAG GTG GTT CCA AAG GCT GAGmRNA CUU GUC CAC CAA GGU UUC CGA CUCAminoAcid Leu Val His Gln Gly Phe Arg Leu
GENETABLE2:MUTANTMC1RGENE(DARKCOAT-COLORPHENOTYPE)
015 022DNA TTG AGG TGG ACG TGT CCG CAA GGAmRNA AAC UCC ACC UGC ACA GGC GUU CCUAminoAcid Asn Ser Thr Cys Thr Gly Val Pro
105 112DNA CGG GAC CGG TGG ACC CAC TGA CACmRNA GCC CUG GCC ACC UGG GUG ACU GUGAminoAcid Ala Leu Ala Thr Trp Val Thr Val
154 161
DNA TCA TAA CAC TGT GAC GGG ACC CGAmRNA AGU AUU GUG ACA CUG CCC UGG GCUAminoAcid Ser Ile Val Thr Leu Pro Trp Ala
209 212
DNA GTG TAC GAG CGTmRNA CAC AUG CUC GCAAminoAcid His Met Leu Ala
230
237DNA GAA CAG GTG GTG CCA AAG GCT GAGmRNA CUU GUC CAC CAC GGU UUC CGA CUCAminoAcid Leu Val His His Gly Phe Arg Leu
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Lesson The Making of the Fittest Natural Selection and Adaptation
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QUESTIONSANSWERKEY1.Ingeneexpression,whichenzymeisresponsiblefortranscribingtheDNAsequenceintomRNAbyaddingcomplementaryRNAnucleotides?RNApolymerase2.Inaeukaryoticcell,wheredoestranscriptionoccur?Inthenucleus3.Describetheprocessoftranslation.TranslationistheprocessofturninginstructionsfrommRNAintochainsofaminoacids.ItoccursinthecytoplasmwiththehelpofribosomesandtRNA.4.Inaeukaryoticcell,whatmainorganelleisinvolvedintranslation?Ribosome5.ExplaintherelationshipbetweenDNAsequence,aminoacidsequence,andproteinstructureandfunction.StudentsmaysimplyrelateDNAsequencetoaminoacidsequence,andaminoacidsequencetothethree-dimensionalshapeoftheprotein.Anexampleofastudentresponsemaybe:“DNAsequenceprovidesthecodefortheaminoacidsequence.Theaminoacidsequencedeterminesthestructureoftheprotein,whichaffectsthefunctionoftheprotein.”6.TheMc1rgenecodesforthemelanocortin1receptor(MC1R)protein.7.IftheMC1Rproteinis317aminoacidslong,whyarethere954basepairsinthecodingregionofthegene?EachoftheaminoacidshasacorrespondingmRNAcodonandDNAtripletconsistingofathree-basesequence.Aproteinthathas317aminoacidsthereforehasaDNAbasesequenceconsistingof951basepairs(317×3=951basepairs).Thethreeadditionalbasepairscorrespondtoastopcodonforwhichthereisnocomplementaryaminoacid.Thestopcodonsignalstheterminationoftranslation.8.OfthefivemutationsyouidentifiedintheMc1rgene,howmanyare: 5substitutions;0insertions;0deletions9.OfthefivemutationsyouidentifiedintheMc1rgene,howmanyare: 1silent;4missense;0nonsense10.Micewiththewild-type(nonmutant)Mc1rgenehavelight-coloredfur.Whichpigmentisresponsibleforthiscoloration?Pheomelanin11.Usingtheinformationintheintroductiononmutationsandyourknowledgeofproteins,developahypothesistoexplainhowthechangesintheMC1Rprotein’saminoacidsequencemightaffectitsfunction.Sampleanswer:ThefourmissensemutationsintheMc1rgenechangetheaminoacidsequenceoftheMC1Rprotein,whichchangesthestructureoftheprotein.Thechangeinproteinstructurewillaffecttheproteinfunction.12.Explainhowsilentmutationsaffectthestructureandfunctionoftheprotein.Silentmutationsdonotchangetheaminoacid,andthereforewillnotchangethestructureoftheprotein.Becauseaprotein’sstructureisrelatedtoitsfunction,silentmutationsdonotaffectthefunctionoftheprotein.13.Usingtheinformationprovidedintheintroductionunder“MC1RGene,”explainhowthemutantMC1Rproteindirectlyaffectsarockpocketmouse’scoatcolor.TheaminoacidchangesintheMC1Rproteinmaychangethestructureandfunctionoftheprotein.Thisleadstoincreasedproductionofeumelanin,whichresultsinthedarkcolor.14.Mutationsareasourceofgeneticvariation.Inthefilm,Dr.Carrollsaysthatmutationsoccurrandomly.Whatdoesthatmean?Sampleanswer:Itmeansthatmutationsdonotoccurforapurposeorforanypredeterminedresult.15.Itisacommonmisconceptionthat“allmutationsarebad.”Usetheexampleofrockpocketmicetoexplainwhythisisnottrue.Inyouranswer,explainhowthedarkcoatcolormutationcanbeanadvantagetosomemiceandadisadvantagetoothers.Sampleanswer:Mutationscanresultinnewtraits.Theselectiveadvantageprovidedbyatraitdependsontheenvironment.Forexample,onalightsubstrate,individualswithdark-coloredcoatswouldbeatadisadvantage
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becausetheywouldstandoutmorethanindividualswithlight-coloredcoats,makingthemeasierforpredatorstospot.However,inthedarklavaflowhabitat,thosesamedark-coloredindividualswouldhaveaselectiveadvantagebecausetheywouldbebettercamouflagedthanlight-coloredindividuals.So,thestatementthat“allmutationsarebad”isincorrect,becausetherearedifferentselectivepressuresonthetraitsproducedbymutationsdependingonthehabitat.Therearealsosilentmutationsthatdonotchangetheresultingprotein;theseareneutral,neithergoodnorbad.16.Useyourunderstandingofevolutionandtheinformationinthefilmtoexplainhowthedark-coloredmutationcametobesocommoninsomepopulationsofrockpocketmice.Bespecific.Sampleanswer:Thedark-coloredmousehasaselectiveadvantageinahabitatsuchasthePinacatelavaflow,whichhasadark-coloredsubstrate.Sincerockpocketmicereproducequicklyandoften,thefrequencyofthisfavoredtraitwouldspreadrapidlythroughthepopulation.Anylight-coloredmiceinthedark-coloredhabitatwouldbeataselectivedisadvantage,thusdecreasingtheirgenefrequencyinfuturegenerations.Inthisway,favorabletraitsaccumulateandincreaseinfrequency—justasDarwinexplained.ANSWERKEYACTIVITY2
GENETABLES
WILD-TYPEMC1RGENE(LIGHT-COLOREDCOATPHENOTYPE) 015 024
DNA TTG AGG TGG GCG TGT CCG CAA GGA GTG GAG
EXTR
ACELLU
LARDO
MAINI
mRNA AAC UCC ACC CGC ACA GGC GUU CCU CAC CUCAminoAcid Asn Ser Thr Arg Thr Gly Val Pro His Leu
MUTANTMC1RGENE(DARK-COLOREDCOATPHENOTYPE) 015 024
DNA TTG AGG TGG ACG TGT CCG CAA GGA GTG GAGmRNA AAC UCC ACC UGC ACA GGC GUU CCU CAC CUCAminoAcid Asn Ser Thr Cys Thr Gly Val Pro His Leu
WILD-TYPEMC1RGENE(LIGHT-COLOREDCOATPHENOTYPE) 105 114
DNA CGG GAC CGG TGG GCC CAC TGA CAC CAT GTC
EXTR
ACELLU
LARDO
MAINIII
mRNA GCC CUG GCC ACC CGG GUG ACU GUG GUA CAG
AminoAcid Ala Leu Ala Thr Arg Val Thr Val Val Gln
MUTANTMC1RGENE(DARK-COLOREDCOATPHENOTYPE) 105 114
DNA CGG GAC CGG TGG ACC CAC TGA CAC CAT GTCmRNA GCC CUG GCC ACC UGG GUG ACU GUG GUA CAGAminoAcid Ala Leu Ala Thr Trp Val Thr Val Val Gln
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WILD-TYPEMC1RGENE(LIGHT-COLOREDCOATPHENOTYPE) 154 163
DNA TCA TAA CAC TGT GAC GGG GCC CGA GCC ACC
INTR
ACELLU
LARDO
MAINI
mRNA AGU AUU GUG ACA CUG CCC CGG GCU CGG UGGAminoAcid Ser Ile Val Thr Leu Pro Arg Ala Arg Trp
MUTANTMC1RGENE(DARK-COLOREDCOATPHENOTYPE) 154 163
DNA TCA TAA CAC TGT GAC GGG ACC CGA GCC ACCmRNA AGU AUU GUG ACA CUG CCC UGG GCU CGG UGGAminoAcid Ser Ile Val Thr Leu Pro Trp Ala Arg Trp
WILD-TYPEMC1RGENE(LIGHT-COLOREDCOATPHENOTYPE) 208 212
DNA CAC GTG TAC GAA CGTTR
ANSM
EMBR
ANEV
mRNA GUG CAC AUG CUU GCAAminoAcid Val His Met Leu Ala
MUTANTMC1RGENE(DARK-COLOREDCOATPHENOTYPE)
208 212DNA CAC GTG TAC GAG CGTmRNA GUG CAC AUG CUC GCAAminoAcid Val His Met Leu Ala
WILD-TYPEMC1RGENE(LIGHT-COLOREDCOATPHENOTYPE) 230 239
DNA GAA CAG GTG GTT CCA AAG GCT GAG TTT CCGINTR
ACELLU
LARDO
MAINIII
mRNA CUU GUC CAC CAA GGU UUC CGA CUC AAA GGCAminoAcid Leu Val His Gln Gly Phe Arg Leu Lys Gly
MUTANTMC1RGENE(DARK-COLOREDCOATPHENOTYPE) 230 239
DNA GAA CAG GTG GTG CCA AAG GCT GAG TTT CCGmRNA CUU GUC CAC CAC GGU UUC CGA CUC AAA GGCAminoAcid Leu Val His His Gly Phe Arg Leu Lys Gly
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QUESTIONSANSWERKEY1.Usingtheaminoacidlocationnumbersprovidedabovethefirstandlastcolumnofeachtable,listthelocationsofthefiveaminoacidsthatcontainamutation.Theaminoacidlocationsare018,109,160,211,and233.2.OfthefivemutationsyouidentifiedintheMc1rgene,howmanyarethefollowing: 5substitutions,0insertions,0deletions3.OfthefivemutationsyouidentifiedintheMc1rgene,howmanyarethefollowing: 1silent,4missense,0nonsense4. a.Whichfouraminoacidlocations(seeQuestion1above)containthemissensemutations?Theaminoacidsare018,109,160,and233.b.ExplainthelinkbetweenDNAsequenceandproteinstructureandfunction.StudentsmaysimplyrelateDNAsequencetoaminoacidsequence,andaminoacidsequencetothethree-dimensionalshapeoftheprotein.More-advancedstudentsshouldbeabletolinkthemutationtoachangeintheprotein’sprimarystructure,whichaffectsotherlevelsofstructure(secondaryandtertiary).AllstudentresponsesshoulddemonstrateanunderstandingofthelinkbetweenDNAandthesequenceofaminoacidsthatdeterminesthestructure,andthereforefunction,ofaprotein.5.Usingtheinformationonmutationsintheintroductionandyourknowledgeofproteins,developahypothesistoexplainhowthechangesintheMC1Rprotein’saminoacidsequencemightaffectitsfunction.StudentsmightsuggestthatsincethefourmissensemutationsintheMc1rgenechangetheaminoacidsequenceoftheMC1Rprotein,theproteinwillnotfunctionproperly,asaprotein’sfunctionisdeterminedbyitsstructure.6.Manyproteins,includingMC1R,containseveralstructuraldomainsthatcanfoldandfunctionindependentlyfromtherest.ThedomainnameswereprovidedforeachportionofDNAsequenceyoutranslatedearlier.Answerthefollowingquestions.a.WhereistheMC1Rproteinfound,andwhatisitsfunction?Bespecific.Itisareceptorproteinembeddedinthemembraneofmelanocytes.Itisspecializedforpigmentproduction.b.WhichproteindomainscontainthefourMc1rmissensemutations?(Refertothegenetablesyoucompletedearlier.)Themutationat018isinExtracellularDomainI,themutationat109isinExtracellularDomainIII,themutationat160isinIntracellularDomainI,andthemutationat233isinIntracellularDomainIII.c.Define“extracellular.”Extracellularmeans“somethingoutsideofacell.”d.Define“intracellular.”Intracellularmeans“somethinginsideofacell.”e.Whyisitsignificantthatthefourmissensemutationsarefoundintheextracellularandintracellulardomainsoftheprotein?Explainyouranswer.(Hint:ThinkaboutMC1R’sfunction.)Specificanswerswillvary,butstudentsshouldhavetheideathataproteinthatspansacellmembranehasaportionthatprojectsoutofthecell(extracellular)andaportionthatprojectsintothecell(intracellular).Thistypeofreceptorproteinusuallyfunctionsineithercelltransportorcellsignaling.Changesinthestructureofextracellularandintracellularportionscanchangethefunctionoftheproteininthesignalingpathwayorthetransportmechanism.(Note:Seethelesson“TheBiochemistryandCellSignalingPathwayoftheMc1rGene”formoredetailonthisconcept.)
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7.UsingtheinformationontheMc1rgeneintheintroductionandyourknowledgeofproteins,developahypothesistoexplainhowthechangeinMC1Rproteinfunctionmightdirectlyaffectarockpocketmouse’scoatcolor.Bespecificandconsiderboththelight-coloredanddark-coloredphenotypes.Specificanswerswillvary,butstudentsshouldsuggestthatthenormalMC1Rreceptorproteinwillproducerelativeamountsofeumelaninandpheomelaninthatwillresultinthelightcoatcolor.Inaddition,thedark-coloredmousepopulationcontainsthemutantMc1rgene,whichresultsinadifferentreceptorprotein.Thischangeinstructuremightleadtoincreasedproductionofeumelanin,whichresultsinthedarkcolor.8.Explainwhythemutationataminoacidlocation211isnotassignificantastheotherfourmutations.Itisasilentmutation,sotheaminoacidinthatpositiondoesnotchange,nordoesthestructureofthespecificdomain.Thisisimportantbecauseaprotein’sstructurerelatestoitsfunction.Nochangeinthestructuresuggeststhatthereisnochangeinthefunctionofthisparticulardomainoftheprotein.9.Mutationsareasourceofgeneticvariation.Inthefilm,Dr.SeanCarrollsaysthatmutationsoccurrandomly.Whatdoesthismean?Sampleanswer:“Itmeansthatmutationsdonotoccurforapurposeorforanypredeterminedresult.”10.Itisacommonmisconceptionthat“allmutationsarebad.”Usetheexampleofrockpocketmicetoexplainwhythisstatementisnottrue.Inyouranswer,explainhowthedarkcoat-colormutationcanbeanadvantagetosomemiceandadisadvantagetoothers.Sampleanswer:“Mutationscanresultinnewtraits.Theselectiveadvantageprovidedbyatraitdependsontheenvironment.Forexample,onalightsubstrate,individualswithdark-coloredcoatswouldbeatadisadvantagebecausetheywouldstandoutmorethanindividualswithlight-coloredcoats,makingthemeasierforpredatorstospot.However,inthedarklavaflowhabitat,thosesamedark-coloredindividualswouldhaveaselectiveadvantagebecausetheywouldbebettercamouflagedthanlight-coloredindividuals.Sothestatementthat“allmutationsarebad”isincorrect,becausetherearedifferentselectivepressuresonthetraitsproducedbymutationsdependingonthehabitat.Therearealsosilentmutationsthatdonotchangetheresultingprotein;theseareneutral,neithergoodnorbad.”11.Useyourunderstandingofevolutionandtheinformationinthefilmtoexplainhowthedark-coloredmutationcametobesocommoninsomepopulationsofrockpocketmice.Bespecific.Sampleanswer:“Thedark-coloredmousehasaselectiveadvantageinahabitatsuchasthePinacatelavaflow,whichhasadark-coloredsubstrate.Sincerockpocketmicereproducequicklyandoften,thefrequencyofthisfavoredtraitwouldspreadrapidlythroughthepopulation.Anylight-coloredmiceinthedark-coloredhabitatwouldbeataselectivedisadvantage,thusdecreasingtheirgenefrequencyinfuturegenerations.Inthisway,favorabletraitsaccumulateandincreaseinfrequency—justasCharlesDarwinexplained.”AUTHORAnnBrokawAPBiologyTeacherRockyRiverHighSchoolRockyRiver,Ohio