Download Educator Materials

UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
OVERVIEW
ThefilmTheBiologyofSkinColorwalksviewersthroughtheprocessbywhichNinaJablonskicametopropose
anexplanationforwhyhumanslivingindifferentpartsoftheworldhavedifferentnaturalskincolors.
Specifically,studentslearnhowpatternsinvariationfortheMC1Rgeneprovideevidencethatdarkskinis
favoredinenvironmentsthatexperienceintenseUVradiation.Asmentionedbrieflyinthefilm,however,
humanskincolorisapolygenictrait.InPart1ofthisactivity,asimplemathematicalmodelillustratesan
idealizedrelationshipbetweenthenumberofgenesinvolvedinatraitandthenumberofphenotypesderived
fromthecombinationofalleles.InPart2,studentslearnaboutthemethodsbywhichgeneticistsidentifyskin
colorgenesandestimateheritability.Finally,inPart3,studentslearnhowgeneticistsanalyzegeneticvariations
totraceanindividual’sancestryanddrawconclusionsaboutthepredominantancestryoftwodifferent
individualsbycomparingtheirgeneticprofilesagainstrealallelefrequencydata.(Thisactivitywasadaptedfrom
lessonplansbytheSmithsonianNationalMuseumofNaturalHistory’s“TeachingEvolutionthroughHuman
Examples”http://humanorigins.si.edu/education/teaching-evolution-through-human-examples.)
KEYCONCEPTSANDLEARNINGOBJECTIVES
•
•
•
•
Scientistsusemathematicalmodelstoestimatethenumberofgenesthataffectatrait.Manydifferent
genescontributetodifferencesinhumanskincolor.
Changestoagene’sDNAsequencecanaffectthetranslationofthegeneintoaminoacids,and
ultimately,thefunctionofaproteinandtheexpressionofatrait.
Bycomparinganindividual’sDNAagainstadatabaseofDNAsequencesfromdifferentpopulations,
scientistscaninferancestry.
Bothgeneticsandtheenvironmentcanaffectexpressionofatrait.Experimentssuggestthedegreeto
whichdifferencesintraitsareinherited.Differencesinhumanskincoloraremostlycontrolledby
genetics.
Studentswillbeableto
•
•
developanduseamathematicalmodeltorepresentarelationshipbetweengenotypesand
phenotypes;and
userealdatatoevaluateandmakeevidence-basedclaims.
CURRICULUMCONNECTIONS
Curriculum
NGSS(April2013)
Practices2,4,7;
HS-LS1-1,HS-LS3-1,HS-LS3-3
APBiology(2012–2013)
SciencePractices1,5;
3.A.1,3.C.1,4.C.2
IBBiology(2016)
3.1,7.2
www.BioInteractive.org
Standards
PublishedAugust2016
Page1of7
UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
KEYTERMS
allele,allelefrequency,gene,genotype,heritability,indigenouspopulation,locus(pl:loci),phenotype,
polygenic,single-nucleotidepolymorphism(SNP)
TIMEREQUIREMENTS
Thislessonwasdesignedtobecompletedwithinasingle50-minuteclassperiodbutmaytakelongerdepending
ontheamountofclassdiscussion.Thisdoesnotincludethe20minutesnecessarytowatchtheshortfilm.
SUGGESTEDAUDIENCE
Thislessonisappropriateforadvancedlevelsofhighschoolbiology,includingAPandIB,aswellasintroductory
collegebiology.
PRIORKNOWLEDGE
•
StudentsshouldhaveabasicunderstandingofMendeliangenetics,includingthetermsDNA,gene,and
allele,andknowthatvariationsinsometraitsareinherited.
•
Itwouldbehelpfulforstudentstohavepriorknowledgeofthetermsgenotypeandphenotypeandhowto
applythetermstospecificexamples.
•
Studentsshouldbecomfortablegeneratingandusingamathematicalexpressionwithtwovariables.
TEACHINGTIPS
•
•
•
Havestudentswatchtheshort(19-minute)filmTheBiologyofSkinColorbeforecompletingthisactivity.If
youdon’thavesufficientin-classtime,considerassigningitashomework.Havestudentswritedownany
questionstheyhavewhiletheywatch.Runthroughsomeofthesequestionsasawarm-uporasa
concludingdiscussion.
Beforebeginningthelesson,considerreviewinggenesandalleleswithstudents.Onewaytoaccomplishthis
istoasktheminanopen-endedclassdiscussiontoeliciteverythingtheyknowaboutgenesandalleles.
Writedowneverythingstudentssaysoallcanseethelist.Attheendofthebrainstormingsession,highlight
thefollowingoverarchingconcepts:
o Genesareinherited.Genesarelocatedonchromosomes.Chromosomesareinheritedinpairs,one
fromeachparent.Differentversionsofgenesarecalledalleles.Asinglegenecanhavemanyalleles.
o Genesaffectphenotypes.Genescodeforproteins,whicharecriticalforthousandsoffunctions
withincells.Theexpressionandactionofproteinsresultinthedistinguishabletraitsofanorganism:
itsphenotypes.
Makesuretoemphasizethecriticalpointthat,whilemuchofthedataforskincolorpresentedinthis
activityfocusesondifferencesamongpeople,comparisonofgenomicsequencesfromindividualsaround
theworldhasrevealedthatallhumansarecloselyrelatedtooneanotherandthatindividualshavemuchin
common.
www.BioInteractive.org
PublishedAugust2016
Page2of7
UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
•
•
Questions1–4askstudentstoanswerquestionsaboutasimplemathematicalmodelofgenotypeand
phenotype,inwhichdifferentgenotypesresultinidenticalphenotypes(forexample,A1A0isequivalentto
A0A1).Ifstudentshavecoveredtheconceptinmathematics,theymayrealizethat,iftheycountedthe
numberofpossiblecombinationsineachgroup,thepatternwouldbelikeeveryotherrowofPascal’s
triangle.Ifyouthinkitisappropriate,tellstudentsthattheycouldusethistriangletopredictthenumberof
individualswithineachgroupiftherewasacrossbetweentwoparentsthatwereheterozygousforeach
allele.
1
1
1
1 gene (3 groups)
1
2
1
1
3
3
1
2 genes (5 groups)
1
4
6
4
1
1
5
10
10
5
1
3 genes (7 groups)
1
6
15
20
15
6
1
Pascal’sTriangle
Youmayconsidercollaboratingwithamathteachertoreinforcetheconceptsofprobabilitythatcan
accompanylearningaboutPascal’striangle.
Part3showsstudentshowinformationaboutthegeneticvariationsunderlyingskincoloramongdifferent
groupsofpeoplecanbeusedtomakeinferencesaboutthelikelygeneticancestryofindividuals.Inactuality,
ancestryinferencesinpeoplearemadeusinghundredstothousandsofSNPsfromlociacrossthehuman
genomeandinvolvingmorethanjustskincolor-relatedgenes.
ANSWERKEY
ACTIVITY1:HOWMANYGENES?
CompletedTable1,withcolorscorrespondingtouniquephenotypes.Black=0pigmentalleles;Brightblue=1;
Red=2;Green=3;Purple=4;Yellow=5;Lightblue=6
Scenario
PossibleGenotypes
Numberof
Unique
Phenotypes
1:Onegene(A)
2:Twogenes
(A,B)
A1A1A1A0A0A1A0A0
3
A1A1B1B1A1A1B0B1A0A1B1B1A0A1B0B1
5
1 1 1 0 1 1 0 0 0 1 1 0 0 1 0 0
AABB
AABB
AABB
AABB
A1A0B1B1A1A0B0B1A0A0B1B1A0A0B0B1
A0A0B1B0A1A0B0B0A0A0B1B0A0A0B0B0
www.BioInteractive.org
PublishedAugust2016
Page3of7
UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
A1A1B1B1C1C1A1A1B1B1C0C1A1A1B0B1C1C1A1A1B0B1C0C1
7
0 1 1 1 1 1 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 1 0 1
AABBCC
AABBCC
AABBCC
AABBCC
A1A1B1B1C1C0A1A1B1B1C0C0A1A1B0B1C1C0A1A1B0B1C0C0
A0A1B1B1C1C0A0A1B1B1C0C0A0A1B0B1C1C0A0A1B0B1C0C0
A1A1B1B0C1C1A1A1B1B0C0C1A1A1B0B0C1C1A1A1B0B0C0C1
A0A1B1B0C1C1A0A1B1B0C0C1A0A1B0B0C1C1A0A1B0B0C0C1
A1A1B1B0C1C0A1A1B1B0C0C0A1A1B0B0C1C0A1A1B0B0C0C0
3:Threegenes
(A,B,C)
A0A1B1B0C1C0A0A1B1B0C0C0A0A1B0B0C1C0A0A1B0B0C0C0
A1A0B1B1C1C1A1A0B1B1C0C1A1A0B0B1C1C1A1A0B0B1C0C1
A0A0B1B1C1C1A0A0B1B1C0C1A0A0B0B1C1C1A0A0B0B1C0C1
A1A0B1B1C1C0A1A0B1B1C0C0A1A0B0B1C1C0A1A0B0B1C0C0
A0A0B1B1C1C0A0A0B1B1C0C0A0A0B0B1C1C0A0A0B0B1C0C0
A1A0B1B0C1C1A1A0B1B0C0C1A1A0B0B0C1C1A1A0B0B0C0C1
A0A0B1B0C1C1A0A0B1B0C0C1A0A0B0B0C1C1A0A0B0B0C0C1
A1A0B1B0C1C0A1A0B1B0C0C0A1A0B0B0C1C0A1A0B0B0C0C0
A0A0B1B0C1C0A0A0B1B0C0C0A0A0B0B0C1C0A0A0B0B0C0C0
1. Thenumberofskincolorgroupsgoesupasthenumberofgenesinvolvedinskincolorincreases.
2. P=2N+1
3. 13
4. P=2(34)+1=69distinctphenotypes
5. DNAistranscribedintomRNAthatis“read,”threenucleotides(acodon)atatime,bytRNA,which
translatesthecodonstoaminoacids.Aminoacidsarestrungtogetherintoapolypeptide,whichis
eventuallyprocessedintoafunctionalprotein.IfachangetoasingleDNAnucleotideresultsinanmRNA
codoncorrespondingtoadifferentaminoacid,thentheoverallstructureandfunctionoftheprotein
mightbechanged.Studentsmayalsomentionthatachangeinaregulatorysequencecouldalterthe
amountofproteinbeingproduced.
6. Sincetheyhaveidenticalgenes,anydifferencesinphenotypewillbeduetoenvironmentaldifferences.
7. Thevalueforheritabilityforskincolorisreportedtobe0.83.Aheritabilityof1.0meansalldifferences
arebecauseofgenetics,andavalueof0.0meansalldifferencesarebecauseoftheenvironment.0.83is
closerto1.0thanto0.0,sotheclaim(“Differencesinhumanskincolorarecausedprimarilyby
differencesingenetics”)issupported.
www.BioInteractive.org
PublishedAugust2016
Page4of7
UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
8. Anenvironmentalfactorsuchasdiet,environmentduringdevelopment,oranyoneofmanyother
factorsmightinhibitorpromotetheactivityoftheproteinsassociatedwithpigmentexpression.
Studentsmayalsomentionhowsunexposurecanaffecttanning,whichisatemporarychangeinskin
color.Sunexposureincreasestheamountofultravioletlightstrikingskincells,whichcausesDNA
damage,whichinturnresultsinchangesintheexpressionofmanygenes.
CompletedProfile1:
Gene
SNPLocus
AlleleFrequencyinIndigenousPopulation
Allele
European
Chinese
Japanese
African
rs1042602
C
0.583
1.0
1.0
1.0
rs1800422
G
0.604
1.0
1.0
0.935
rs1126809
G
0.783
1.0
1.0
1.0
rs1408799
C
0.30
0.989
0.978
0.775
rs2733832
C
0.367
0.989
0.977
0.933
rs1800401
C
0.935
1.0
1.0
0.979
rs1800407
G
0.933
1.0
1.0
1.0
rs1800414
A
1.0
0.367
0.477
1.0
rs12913832
T
0.208
1.0
1.0
1.0
rs26722
G
1.0
0.611
0.591
0.95
rs16891982
C
0.983
0.011
0.0
0.0
SLC24A5
rs1426654
G
0.0
0.989
0.989
0.975
KITLG
rs642742
A
0.136
0.267
0.114
0.922
TYR
TYRP1
OCA2
SLC45A2
9. Basedonthisprofile,theindividualismostlikelytobepredominantlyofChineseancestry.Nineofthe
13allelesarepresentinthehighestfrequencyamongindigenousChinesepopulations,theCalleleof
rs16891982isnotpresentintheindigenousJapaneseorAfricanpopulations,andtheGalleleof
rs1426654isnotpresentintheindigenousEuropeanpopulation.Youmaywishtohighlightthatwith
thesedataalone,itisdifficulttoexcludeJapaneseancestryforthisindividual.Thedifferencesbetween
theChineseandJapaneseallelefrequenciesfortheseSNPsareaboutonepercentforthethreealleles
thatarehigherintheChinesepopulation.Additionally,whiletheCalleleofrs16891982isnotpresentin
theindigenousJapanesepopulation,thealleleisonlyatonepercentintheChinesepopulation.
Samplingerrormayexplainthedifferencebetweenfrequenciesinthetwogroups.
www.BioInteractive.org
PublishedAugust2016
Page5of7
UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
CompletedProfile2:
Gene
SNPLocus
AlleleFrequencyinIndigenousPopulation
Allele
European
Chinese
Japanese
African
rs1042602
C
0.583
1.0
1.0
1.0
rs1800422
G
0.604
1.0
1.0
0.935
rs1126809
G
0.783
1.0
1.0
1.0
rs1408799
T
0.70
0.011
0.022
0.225
rs2733832
C
0.367
0.989
0.977
0.933
rs1800401
C
0.935
1.0
1.0
0.979
rs1800407
G
0.933
1.0
1.0
1.0
rs1800414
G
0.0
0.633
0.523
0.0
rs12913832
T
0.208
1.0
1.0
1.0
rs26722
A
0.0
0.389
0.409
0.05
rs16891982
G
0.017
0.989
1.0
1.0
SLC24A5
rs1426654
G
0.0
0.989
0.989
0.975
KITLG
rs642742
G
0.864
0.733
0.886
0.0778
TYR
TYRP1
OCA2
SLC45A2
10. ThisindividualismostlikelyofpredominantlyJapaneseorChineseancestry.Nineofthe13allelesare
foundatthehighestfrequenciesamongindigenousChinesepopulations,and10ofthe13allelesare
foundatthehighestfrequenciesamongindigenousJapanesepopulations.Inaddition,neitherofthese
indigenouspopulationscanbeexcludedusingthisparticulardataset.Liketheanswerfortheprevious
individual,itisdifficulttodistinguishbetweentheJapaneseandChinesepopulationsusingthisdataset.
11. ACalleleatrs12913832ismoreusefulbecauseitisfoundin79.2%ofindividualsinindigenous
Europeanpopulationsbut0%ofindividualsinindigenousChinese,Japanese,orAfricanpopulations.On
theotherhand,aCalleleatrs1042602isfoundamong100%ofindividualsinindigenousJapanese,
Chinese,andAfricanpopulationsandmorethanhalf(58.3%)ofpeopleinindigenousEuropean
populations.TheCalleleisthereforesowellconservedamongthesepopulationsthatitisnotusefulin
helpingtodeterminelikelyancestry;individualswithancestryofeachofthefourpopulationsareeither
guaranteedorlikelytohavetheallele.
12. AdditionalSNPlociwithallelespresentatdifferentfrequenciesamongindigenousJapaneseandChinese
populationscouldhelpdistinguishtheancestryofthepersonwithProfile2.
www.BioInteractive.org
PublishedAugust2016
Page6of7
UNDERSTANDINGVARIATION
INHUMANSKINCOLOR
EducatorMaterials
13. Answerswillvary.Itismostimportantthatstudentsjustifytheirthinkingandshowthatthey
understandthatcertainallelescanruleoutaparticularindigenouspopulation;forexample,theGallele
atrs1426654rulesoutEuropeanancestry.TheSNPrs642742islesshelpfulatdeterminingancestry
becausebothallelesarepresentinallpopulations.
14. Anindividualcanhaveavariedancestryifnotalloftheirancestorswerefromthesameindigenous
populations—thatis,ifsomerelativesweretheresultofanindividualfromoneindigenousgrouphaving
childrenwithpeoplefromanothergroup.
REFERENCES
ThisactivityisadaptedfromanactivityintheEvolutionofHumanSkinColorcurriculumunitforAPBiologythat
isapartoftheSmithsonianInstitution’sNationalScienceFoundation-fundedTeachingEvolutionthrough
HumanExamplesproject(GrantNo.1119468).Seehttp://humanorigins.si.edu/education/teaching-evolutionthrough-human-examplestoexplorethefullcurriculumunit.
ClarkP.,StarkA.E.,WalshR.J.,JardineR.,MartinN.G.“Atwinstudyofskinreflectance,”AnnalsofHuman
Biology8(1981):529–541.
KlugW.S.,CummingsM.R.,Spencer,C.A.ConceptsofGenetics.(NewYork:Pearson,2006).
SturmR.A.,DuffyD.L.“Humanpigmentationgenesunderenvironmentalselection,”GenomeBiology13(2012):
248.doi:10.1186/gb-2012-13-9-248.
SturmR.A.“Moleculargeneticsofhumanpigmentationdiversity,”HumanMolecularGenetics18(2009):R9–
R17.doi:10.1093/hmg/ddp003.
The1000GenomesProjectConsortium.“Aglobalreferenceforhumangeneticvariation,”Nature526(2015):
68–74. doi:10.1038/nature15393.
AUTHORS
WrittenbyPaulBeardsley,CalPolyPomona.EditedbyK.DavidPinkerton,educationalconsultant;Stephanie
Keep,educationalconsultant;andMelissaCsikari,HHMI.CopyeditedbyLindaFelaco.
SCIENTIFICREVIEWERS
RebeccaLamason,UniversityofCalifornia,Berkeley;andKathrynJones,HowardCommunityCollege.
www.BioInteractive.org
PublishedAugust2016
Page7of7