Download DIET AND THE EVOLUTION OF SALIVARY AMYLASE

Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
DIETANDTHEEVOLUTIONOFSALIVARYAMYLASE
INTRODUCTION
Overthe200,000yearsorsothatmodernhumanshaveexisted,humanpopulationshaveadaptedtoawide
rangeofenvironments,includingdifferentfoods.Theavailabilityofnewenergy-richfoodshasresultedin
differentselectionpressuresaffectinghumanevolution.Forexample,whensomehumanpopulationsstarted
consumingmilkasadults,theabilitytodigestlactose,thesugarinmilk,providedasurvivaladvantageto
individualswiththetrait.Overtime,thelactose-tolerancetraitincreasedinfrequencyinsomehuman
populations.
Anotherexampleofanevolutionarilyimportantchangeindietwastheincreasedavailabilityofstarch-richfoods,
beginningwiththeagriculturalrevolutionabout10,000yearsago.Oncestarch-richfoodsbecamecommon
staplesinthehumandiet,peoplewhowereabletoeffectivelydigeststarchmayhavehadasurvivaladvantage.
Starchisaplantpolysaccharidecomposedofmanybuildingblocksofglucose,whichisamonosaccharide.Starch
cannotbedissolvedinwaterorinstomachacidsoanenzymeisneededtobreakitup.Starchdigestionbeginsin
themouthwiththeenzymeamylase.Salivaryamylasebreaksthecovalentbondsbetweenglucoseunitsin
starchbyaddingawatermolecule;thischemicalreactioniscalledhydrolysis.Thereactionproducesmaltose,a
glucose-glucosedisaccharide.Maltoseisfurtherbrokendownintoglucoseinthesmallintestinebytheenzyme
maltase.
Figure1.Stepsincarbohydrate
digestion.Carbohydrate
digestionbeginsinthemouth,
wheresalivaryα-amylase
attackstheα-glycosidiclinkages
instarch,themain
carbohydrateingestedby
humans,toproducemaltose.
Theenzymeα-amylaseisalso
producedinthepancreas
(pancreaticα-amylase)and
dispensedtothesmall
intestine,whereitconvertsany
remainingstarchmoleculesto
maltose.Maltoseisthen
cleavedintotwoglucose
moleculesbymaltase.
Monosaccharides,suchas
glucose,areabsorbedthrough
thewallofthesmallintestine
intothebloodstream.
PublishedOctober2013
www.BioInteractive.org
UpdatedFebruary2017
Page1of7 Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
Inhumans,theAMY1geneonchromosome1producessalivaryamylase.Humansarediploidorganisms,
meaningthat,exceptforthegenesontheXandYchromosomes,theyhavetwocopiesofmostgenes—one
copyinheritedfromeachparent.However,geneticstudiesshowthatpeoplecanhaveanywherefromtwoto15
diploidcopiesoftheAMY1geneoneachchromosome1,suggestingthatthegenehasbeenduplicatedduring
humanevolution.Whywouldthisbe?
ResearcherGeorgePerryandhiscolleagueshypothesizedthatassomegroupsofpeoplestartedconsuming
morestarch,individualswithmorecopiesoftheAMY1genewouldhavehadasurvivaladvantage.Itfollowsthat
peoplelivinginpopulationswithstarch-richdietswouldhavemorecopiesoftheAMY1genethanpeoplein
populationsthatdon’teatalotofstarch-richfoods(G.H.Perryetal.,NatureGenet.2007).
QUESTIONS
1.Listtheenzymesinvolvedinstarchdigestion,wheretheywork,andwhattheydo.
2.Namethegenethatproducessalivaryamylase.Howmanycopiesofthegenedohumanshave?
3.Theresearchershypothesizedthatincreasedconsumptionofstarch-richfoodsduringhumanevolutionary
historygaveindividualswithmultiplecopiesofthesalivaryamylasegenean“advantage.”Inthiscontext,what
doesadvantagemean?
Totesttheirhypothesis,PerryandcolleaguesanalyzedDNAcollectedfromtwogroups.Thefirstgroupconsisted
ofpopulationsthathavehistoricallyconsumedadietrichinproteinandlowinstarch,suchashunter-gatherers
livingintropicalrainforestsorneartheArcticCircle.Theothergroupconsistedofpopulationsfromagricultural
societiesandhunter-gathererslivinginaridenvironments,whichtraditionallyeathigh-starchfoods.The
researchersmeasuredthenumberofcopiesoftheAMY1geneinindividualsfromthesedifferentpopulations.In
thisactivity,youwillanalyzesomeofthedatacollectedbyPerryandcolleagues.
MATERIALS
•
•
Scientificcalculatorand/oracomputerwithaspreadsheetprogramlikeExcel
Graphpaper,pencils,andarulerifnotusingaspreadsheetprogram
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PublishedOctober2013
UpdatedFebruary2017
Page2of7 Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
PROCEDURE
PartA.RelationshipBetweenAMY1CopyNumberandAmylaseProduction
BeforelookingatAMY1copynumberindifferentpopulations,Perryandcolleaguesinvestigatedwhetherthe
numberofcopiesoftheAMY1geneisassociatedwiththeamountofamylaseinsaliva.ThedatainTable1show
thenumberofAMY1genecopiesindifferentindividualsandthemilligrams(mg)ofAMY1proteinpermilliliter
(ml)ofsaliva.Thesemeasurementsweretakenin25adultAmericansofEuropeandescent.(Source:G.H.Perry
etal.,NatureGenet.2007.)
Table1.AMY1CopyNumberandAmylaseProductionAmongEuropean-AmericanPopulations
Individual
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
NumberofAMY1Gene
Copies
7
5
12
6
8
6
7
11
6
3
8
5
5
7
9
7
6
6
3
4
7
8
8
4
7
AMY1ProteininSaliva(mg/ml)
3.85
1.09
5.17
3.24
2.80
3.30
2.89
3.76
2.65
0.93
2.46
1.37
2.33
3.37
3.72
5.67
4.61
4.33
3.13
4.24
4.33
1.89
3.48
1.83
3.41
PublishedOctober2013
www.BioInteractive.org
UpdatedFebruary2017
Page3of7 Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
1.ThedatainTable1showthenumberofAMY1genecopiesandmilligramsofamylaseproteinpermilliliterof
salivain25adults.Onaseparatesheetofpaper,constructandlabelagraphthatillustratestherelationship
betweenthesetwomeasuredvariables.Includeatitleforyourgraphandlabelsforthex-andy-axes.
2.Fromthegraph,dothetwovariablesappeartobeassociated?Explainyouranswer.
3.Basedonthegraph,makeaclaimregardingthenumberofAMY1genecopiesandhowtheyrelatetothe
concentrationofAMY1proteininsaliva.Explaintheclaimusingscientificreasoning.
4.Basedonyourclaim,suggestahypothesistoexplainwhymoreorfewercopiesofagenewouldaffectthe
amountofproteinproduced.
5.SupposethatyouanalyzedthenumberofcopiesoftheAMY1geneintwoindividuals.IndividualAhasfour
diploidcopiesoftheAMY1gene,andindividualBhaseightdiploidcopiesoftheAMY1gene.Canyousaywith
certaintywhowillhavemoreamylaseenzymeintheirsaliva?Useevidencefromyourgraphand/orTable1to
supportyouranswer.
PublishedOctober2013
www.BioInteractive.org
UpdatedFebruary2017
Page4of7 Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
PartB:RelationshipBetweenAMY1CopyNumberandDietaryStarch
Table2showssomeofthedataPerryandcolleaguescollectedonAMY1genecopynumbersfromdifferent
populations.Thefirstgroupofindividualsstudiedincluded11adultAmericansofEuropeandescent,sixHadza
(Tanzania),andeightJapanese,allofwhomeatahigh-starchdiet.Thesecondgroupofindividualsstudied
includednineBiaka(CentralAfricanRepublic),sixMbuti(DemocraticRepublicofCongo),eightYakut(Siberia),
andtwoDatog(Tanzania),allofwhomeatalow-starchdiet.(Source:G.H.Perryetal.,NatureGenet.2007.)
Table2.AMY1CopyNumberandDietaryStarchLevels
High-StarchDietProfile
Low-StarchDietProfile
#ofAMY1
GeneCopies
4
8
11
6
5
6
6
15
8
8
7
15
5
7
6
3
7
10
6
6
5
6
5
6
7
Population
European-American
European-American
European-American
European-American
European-American
European-American
European-American
European-American
European-American
European-American
European-American
Hadza
Hadza
Hadza
Hadza
Hadza
Hadza
Japanese
Japanese
Japanese
Japanese
Japanese
Japanese
Japanese
Japanese
Population
Biaka
Biaka
Biaka
Biaka
Biaka
Biaka
Biaka
Biaka
Biaka
Mbuti
Mbuti
Mbuti
Mbuti
Mbuti
Mbuti
Yakut
Yakut
Yakut
Yakut
Yakut
Yakut
Yakut
Yakut
Datog
Datog
#ofAMY1
GeneCopies
8
4
2
5
4
4
6
7
4
4
7
4
4
5
4
9
4
5
5
9
10
8
5
2
8
1.ThedatainTable2representthenumberofAMY1genecopiesintwogroupswithdifferentdiets.Foreach
diet-profilegroup(i.e.high-starchorlow-starch),determinethesamplesizeandthencalculatethemean,
standarddeviation,and95%confidenceinterval.Enteryouranswersintheboxbelow.
PublishedOctober2013
www.BioInteractive.org
UpdatedFebruary2017
Page5of7 Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
Note:ThemeanyouwillcalculatebelowistheaveragenumberofAMY1genecopiesforthatgroupand
providesanestimateoftheaveragegenecopynumberoftheentirehigh-starchorlow-starchdietpopulation.
Toknowhowclosethissamplemeanistotheactualmeanofthewholepopulationyoucancalculatethe95%
confidenceinterval.Basicallythe95%confidenceintervaltellsyouthattheactualpopulationmeanislikelytobe
avaluewithinthatinterval.Theformulaprovidedbelowforcalculatingthe95%confidenceintervalisan
approximationoftheactualformula.Youmayuseacalculatororspreadsheetprogramtocalculate95%
confidenceintervals,whichwillgiveyouaslightlydifferentresult.
High-StarchDietProfile
Low-StarchDietProfile
SampleSize(n)
Mean(𝒙)
StandardDeviation(s)
95%ConfidenceInterval
𝟐𝒔
𝒏
2. Onaseparatesheetofpaper,constructandlabelagraphthatsummarizesthedatainTable2.Include
95%confidenceintervalerrorbarsaswellasatitleforyourgraphandlabelsforthex-andy-axes.
3. Fromthegraph,howdothetwodietprofilescompare?Explainyouranswer.
4. Suggestascientifichypothesis(atestableexplanation)toexplainyouranswertoquestion3above.
PublishedOctober2013
www.BioInteractive.org
UpdatedFebruary2017
Page6of7 Short Film
Got Lactase? The Co-evolution of
Genes and Culture
Student Handout
MathExtensionforPartA(Optional)
JustlookingandexploringthegraphallowedyoutomakeclaimsabouttherelationshipbetweenAMY1gene
copynumberandsalivaryamylaseproduction.Statisticaltestsareusedtoprovidesupportingevidenceforthe
claimbyestimatinguncertainty.
1.UsePearson’scorrelationcoefficientfromalinearregressiontesttotestthenullhypothesisthatthesetwo
variableslistedinTable1arenotcorrelated(r=0).Whatdoyouconcludebasedonyourcalculations?
2.UseastatisticaltesttodeterminethestrengthofthecorrelationbetweenAMY1genecopynumberand
salivaryamylaseproduction.Whatdoyouconcludebasedonyourcalculations?
MathExtensionforPartB(Optional)
Thegraphssuggestthatpopulationsthatconsumeahigh-starchdietandpopulationsonlow-starchdietshavea
differentnumberofcopiesoftheAMY1gene.
1.Performat-testtofindoutwhetherthisdifferenceisrealandnotsimplyduetochance.Explainyourresults.
2.Basedonthedataandstatistics,makeaclaimregardingwhatmightexplainthedifferenceinAMY1copy
numberbetweenthetwogroupsofpopulations.
PublishedOctober2013
www.BioInteractive.org
UpdatedFebruary2017
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