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CLASS4-16March:GENE
1. Historyoftheconcept2. Geneasinformation3. Genesanddevelopment4. Genesandevolution
Bibliography:sentorcited
FORMATERIAL,SENDEMAILTO:dvecchi@fc.ul.pt
Enrolment:GabinetedeEstudosPos-graduados 1
1.1Prehistory
Onlyinthenineteenthcenturyhereditybecameamajorproblemtobedealtwithinbiology:why?
Whatwasknownfrombreedingexperimentsisthatthereweretwokindsofvariations:fluctuating/quantitativechanges(deviationfromnormaltrait)anddiscontinuous/qualitativeones(appearanceofqualitativelynewtraits).Alltherestwasamatterofdebate(cytologyorcellbiologywasdeveloping).
Twomainsetsofproblems1. Natureoftheunitsofheredity:localisationinthebody;material
constitution(whatkindofstuffandwhatkindofstructure);2. Mechanismoftransmissionfromonegenerationtotheother. 2
1.2Pre-history:transmissionview
Natureoftheunitsofheredity:localisationinthebody;materialconstitution(whatkindofstuffandwhatkindofstructure);
“BIOLOGYhasevidentlyborrowedtheterms‘heredity’and‘inheritance’fromeverydaylanguage,inwhichthemeaningofthesewordsisthe‘transmission’ofmoneyorthings,rightsorduties—orevenideasandknowledge…Hippocrates….suggestedthatthedifferentpartsofthebodymayproducesubstanceswhichjoininthesexualorgans,wherereproductivematterisformed.Darwin’shypothesisof‘pangenesis’isinthispointveryconsistentwiththeHippocraticview…AlsotheLamarckianviewastotheheredityof‘acquiredcharacters’isinaccordancewiththoseoldconceptions.”JohannsenW.TheGenotypeConceptionofHeredity.TheAmericanNaturalist1911;45:129-159.p.989
WhatisJohannsensuggestingasanalternativeview?3
1.3Pre-history:Darwin’spangenesis
Natureoftheunitsofheredity:localisationinthebody;materialconstitution(whatkindofstuffandwhatkindofstructure);
Pangenesis
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1.4Pre-history:Darwin’spangenesis
Natureoftheunitsofheredity:localisationinthebody;materialconstitution(whatkindofstuffandwhatkindofstructure);
ReactiontoDarwin’spangenesishypothesis:
-FrancisGalton:gemmulesarenotcirculatingthroughbloodstream(experimentswith88rabbitswith“noalterationofbreed”asaresult);-DeVries:unitsofhereditystayinthecells;-AugustWeismann:transmissionfromsomatictissuetogerminaltissuedoesnothappen;
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1.5Prehistory:whatkindofstuff
Natureoftheunitsofheredity:localisationinthebody;materialconstitution(whatkindofstuffandwhatkindofstructure);
-HerbertSpencer:unitsofheredityareentitieswithadimensionbetweenmoleculesandcells;-AugustWeismann:localisationinthenucleusofthecell,specificallyinthechromosomes;chromatinparticlesarebearersofspecialorganisingfunctionsindevelopment:
-RediscoveryofGregorMendel’swork
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1.6Prehistory:Mendelism
Mendel:
FavouritetheoryofinheritanceatthetimeofMendel:blendinginheritance(vsparticulate;i.e.,theideathatcharactersfromparentsareinheritedinamixedformbyoffspring;theproblemofthisviewwashowtoexplaintheappearanceofqualitativelynewvariantsnotpresentinpreviousgenerations)+inheritanceofacquiredtraits(e.g.,transmissionmodelofinheritance:personalqualitiesofindividualorganismcausethequalitiesofitsoffspring).
Peaplantshavemanydichotomoustraits(notcompatiblewithblendinginheritance).
Startwithtruebreedinglines(whicharegeneticallypureormonistic,withjustonetypeofallelepertrait);createmono-hybridcrossbycross-fertilisingtwogardenpeaplantswithdichotomoustraitsandseewhathappens. 7
1.7Prehistory:Mendelism
ParentalGeneration:Purple&WhiteflowersFilialGeneration1:PPPP(disappearanceoftrait….explainedbydominance)FilialGeneration2:PPPW(reappearanceinthesameproportion…explainedbyreappearanceofrecessivetrait)
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1.8Prehistory:Mendelism
Mendel:
Homozygous(2allelesofthesametype)vsheterozygousorganisms;
PP–purpleG/PmapPp–purpleG/Pmappp–whiteG/Pmap
1TO2TO1RATIO
LAWOFSEGREGATION:allelepairsseparateduringgameteformation,andrandomlyuniteatfertilisation.
LAWOFINDEPENDENTASSORTMENT:individualhereditaryfactorsassortindependentlyduringgameteproduction,givingdifferenttraitsanequalopportunityofoccurringinnextgeneration.
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1.9Prehistory:Mendelism
RediscoveryofMendel’sworkin1900byHugodeVries,CarlCorrens,andErichTschermak.Newparadigmofinheritance:
1.Heritablefactor(differentversionsofthegene,e.g.,allele)responsibleforappearanceoftrait;2.Indiploidorganisms(i.e.,havingtwohomologouschromosomesineachcell)thereare2alleles/particles/heritablefactorsforeachtrait;3.Oneallelecouldbedominantandtheotherrecessive;4.Whengametesareformedbyparentsinpreparationforsexualreproduction,thegametesgetonlyoneofthetwoforms;hence50%chance;5.Allelesaretheheritablefactors,notthepersonalqualities(i.e.,themorphological,physiologicalandbehaviouralmanifestationsoftheheritablefactors,thatis,thephenotypes)oforganisms;6.Allelesareparticulate,discreteobjects(vsblendinginheritance). 10
1.10Pre-history:genotypeconception
“Thepersonalqualitiesofanyindividualorganismdonotatallcausethequalitiesofitsoffspring;butthequalitiesofbothancestoranddescendantareinquitethesamemannerdeterminedbythenatureofthe‘sexualsubstances’—i.e.,thegametes—fromwhichtheyhavedeveloped.Personalqualitiesarethenthereactionsofthegametesjoiningtoformazygote;butthenatureofthegametesisnotdeterminedbythepersonalqualitiesoftheparentsorancestorsinquestion.Thisisthemodernviewofheredity.”
Genotypeconceptionofheredity:“…Ihaveproposedtheterms“gene”and“genotype”andsomefurtherterms,as“phenotype”…tobeusedinthescienceofgenetics.The“gene”isnothingbutaveryapplicablelittleword,easilycombinedwithothers,andhenceitmaybeusefulasanexpressionforthe“unit-factors,”“elements”or“allelomorphs”inthegametes,demonstratedbymodernMendelianresearches.A“genotype”isthesumtotalofallthe“genes”inagameteorinazygote.…….phenotypesarerealthings…”
JohannsenW.TheGenotypeConceptionofHeredity.TheAmericanNaturalist1911;45:129-159.pp.990+991 11
1.11Genotypeconception:issues
Twomainsetsofproblems:Natureoftheunitsofheredity:localisationinthebody;materialconstitution(whatkindofstuffandwhatkindofstructure);Mechanismoftransmissionfromonegenerationtotheother.
3basicdistinctionsconcerningnatureofgenes:1. germvssoma(Weismann);2. discretevscontinuousgeneticfactors(Mendel);3. genesvsphenotypes(Johannsen).
Pendingissues:• Localizationinthecell;• Mechanismofinheritance;• Deploymentindevelopment.
“Astothenatureofthe‘genes’itisasyetofnovaluetoproposeanyhypothesis;butthatthenotion“gene”coversarealityisevidentfromMendelism….”JohannsenW.TheGenotypeConceptionofHeredity.TheAmericanNaturalist1911;45:129-159.pp.990+991 12
2.1Fromtheoreticalentitiestomaterialones
ThomasHuntMorganandthefruitflyDrosophilamelanogastergroup.
Geneslocatedinalinearorderalongthedifferentchromosomes(like"beadsonastring”,Morgan,T.H.,1926.Thetheoryofthegene,NewHaven:YaleUniversityPress.p.24)
Morgan’sprogrammewasformal,thusagnosticconcerningmaterialnatureofgenesandcomplexityofG-Pmap(i.e.,the“genotype-phenotypemap”;seeRheinberger,Müller-WilleandMeuniersection2).
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Interlude:thegenotype-phenotypemapasabijecsvefuncson—>everygenecausesonephenotypeindevelopment
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1.samegenotypeassociatedwithseveralphenotypes(i.e.,pleiotropy,forinstancerepresentedbyG1influencingdevelopmentofP1,P2,andP3);2.severalgenotypesassociatedwiththesamephenotype(i.e.,polygeniccontrolofdevelopment,representedbyP2beinginfluencedbyG1,G2andG3);3.samegenotypeassociatedwithdifferentphenotypesindifferentenvironments(aformofenvironmentalcontrolofgeneexpression,representedbyG1influencingdevelopmentofP1inenvironmentE1andP4inenvironmentE2);4.differentgenotypesinthesameenvironmentproducingsamephenotype(aformof“environmentaldeterminason”ofphenotype,representedbyG2andG3influencingdevelopmentofP3inenvironmentE3)
Interlude:thegenotype-phenotypemapasacomplexfuncson
2.2Fromtheoreticalentitiestomaterialones
Aimofclassicalgenetics:findingaformalcorrelationbetweenindividualgenes(characterisedasspecificlocionthechromosomes)withcertaincharacters.
Veryimportantfordevelopmentofmathematicalpopulationgenetics:“…RonaldA.Fisher,J.B.S.Haldane,andSewallWrightcouldmakeuseoftheclassicalgenewithequalrigorandprecisiontoelaboratetestablemathematicalmodelsdescribingtheeffectsofevolutionaryfactorslikeselectionandmutationonthegeneticcompositionofpopulations(Provine1971).Asaconsequence,evolutionbecamere-definedasachangeofgenefrequenciesinthegenepoolofapopulation…“(seeRheinberger,Müller-WilleandMeuniersection2). 16
2.3Genesinpopulationgenetics
“ScottGilbert(2000)hassingledoutsixaspectsofthenotionofthegeneasithadbeenusedinpopulationgeneticsuptothemodernevolutionarysynthesis.First,itwasanabstraction,anentitythathadtofulfillformalrequirements,butthatdidnotneedtobeandindeedwasnotmateriallyspecified.Second,theevolutionarygenehadtoresultinorhadtobecorrelatedwithsomephenotypicdifferencethatcouldbe“seen”ortargetedbyselection.Third,andbythesametoken,thegeneoftheevolutionarysynthesiswastheentitythatwasultimatelyresponsibleforselectiontooccurandlastacrossgenerations.Fourth,thegeneoftheevolutionarysynthesiswaslargelyequatedwithwhatmolecularbiologistscametocall“structuralgenes.”Fifth,itwasageneexpressedinanorganismcompetingforreproductiveadvantage.Andfinally,itwasseenasalargelyindependentunit.”(seeRheinberger,Müller-WilleandMeuniersection4) 17
2.4Genesasautocatalyticandheterocatalytic
HermanJ.Muller:genesasmaterialparticles:
“Mullersawgenesasfundamentallyendowedwithtwoproperties:thatofautocatalysisandthatofheterocatalysis.Theirautocatalyticfunctionallowedthemtoreproduceasunitsoftransmissionandthustoconnectthegenotypeofonegenerationtothatofthenext.Theirconcomitantcapabilityofreproducingmutationsfaithfullyoncetheyhadoccurredgaverise,onthisaccount,tothepossibilityofevolution.Theirheterocatalyticcapabilitiesconnectedthemtothephenotype,asunitsoffunctioninvolvedintheexpressionofaparticularcharacter.Withhisownexperimentalwork,Mulleraddedasignificantargumentforthematerialityofthegene,pertainingtothethirdaspectofthegeneasaunitofmutation.In1927,hereportedontheinductionofMendelianmutationsinDrosophilabyusingX-rays.”(Rheinberger,Müller-WilleandMeuniersection2). 18
2.5Geneasautocatalyticentities
Muller:genesasautocatalyticentitiesableofself-replicationthusexplainingthemechanismofinheritance.
GenesareDNAmolecules,notproteins:OswaldAvery,ColinMacLeod,andMaclynMcCarty1944
DNAstructureasadoublehelix:FrancisCrickandJamesD.Watson1953
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2.6Geneasautocatalyticentities
FrederickGriffith’sexperiment(1928):
TypeII-R(nonvirulent)strainsofbacteria—>nodeadmice
TypeIII-S(virulent)strain—>deadmice
KillbyheatbacteriaoftypeIII-Sstrain—>nodeadmice
Mixheat-killedtypeIII-SstrainwithtypeII-Rstrain—>deadmice
WhatmolecularagentisresponsibleforTRANSFORMATIONoftypeII-R(nonvirulent)strainbacteriaintotypeIII-S(virulent)ones?Proteinsorsomeothermolecularagent?
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2.7Geneasautocatalyticentities
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Averyetal.experiment1944
OnlyintheculturetreatedwithDNasedidtheSstrainbacteriafailtogrow;noDNA=notransformason—>genes=DNAstuff
cf.hzps://ib.bioninja.com.au/higher-level/topic-7-nucleic-acids/71-dna-structure-and-replic/dna-experiments.html
2.8Geneasautocatalyticentities
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2.9Geneasautocatalyticentities
DNAasgeneticmaterial:butwhataboutitsstructure?DNAasdoublehelix:FrancisCrickandJamesD.Watson1953(slide2.8).
Andhowcanithaveautocatalyticproperties?MatthewMeselsonandFranklinStahlin1958:DNAreplicatessemi-conservatively(cf.https://www.nature.com/scitable/content/the-meselson-stahl-experiment-18551/). 23
2.10Geneasautocatalyticentities
Muller:genesasautocatalyticentitiesableofself-replicationthusexplainingthemechanismofinheritance.
GenesareDNAmolecules,notproteins:OswaldAvery,ColinMacLeod,andMaclynMcCarty1944
DNAasdoublehelix:FrancisCrickandJamesD.Watson1953
DNAreplicatingsemi-conservatively:MeselsonandStahl1958
“…thestructureoftheDNAdoublehelixhadallthecharacteristicsthatweretobeexpectedfromamoleculeservingasanautocatalytichereditaryentity…“(Rheinberger,Müller-WilleandMeuniersection3).
Butaregenestrulyself-replicating? 24
3.1Themoleculargeneanddevelopment
Genesasheterocatalyticentities(slide2.4)causallyassociatedwithparticularphenotypes:-onetoonemapping(Morgan’sschool);-onegenexforoneenzyme(GeorgeBeadleandEdwardTatum);-genesareinformationalunitsthatdeterminedevelopmentaloutcomes.
WatsonandCrickpopularisedinformationtalkingenetics.TheyhypothesisedthatgenesmightbeencodedintheDNAmolecule,morepreciselyinthenucleotides:
“…inalongmolecule,manydifferentpermutationsarepossible,anditthereforeseemslikelythattheprecisesequenceofthebasesisthecodewhichcarriesthegeneticalinformation.”(Watson,J.D.&Crick,F.H.(1953).MolecularStructureofNucleicAcids:astructurefordeoxyribosenucleicacid.Nature,171(4356):737–738.,p.964)
Sequencehypothesis:“…thesequenceofbasesdeterminesthesequenceofaminoacidsoftheproteinbeingsynthesized”.(Crick,F.(1958)OnProteinSynthesis.TheSymposiaoftheSocietyforExperimentalBiology,12,138-163.,p.158)
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3.2Themoleculargeneasinformation
Theontologicalfoundationoftheinformationalinterpretationisadoublereification:
1. ofgeneticinformationasanon-physicalentity;
2. ofinformationalspecificityasanon-physicalformofspecificity.
Williams(1966)proposedacyberneticconceptionofthegenethatmakesitindependentofitsmolecularsubstrate:
“AgeneisnotaDNAmolecule;itisthetranscribableinformationcodedbyamolecule....thegeneisapacketofinformation,notanobject.”(Williams,G.C.(1992).NaturalSelection:Domains,Levels,andChallenges.OxfordUniversityPress,p.11)
“...heredityisconcernedwiththetransmissionofinformation,notjustofmatterorenergy.”(J.Maynard-Smith2001.Theconceptofinformationinbiology.PhilosophyofScience,67:177-194p.182)
3.3Themoleculargeneasinformation
“If[eyeless]isactivatedinadevelopingleg,thenaneyedevelopsatthesite....Thissuggeststhatthegeneissendingasignal,'makeaneyehere'...”
J.Maynard-Smith2001p.188
InductionofectopiceyestructuresinDrosophila.
3.4Themoleculargeneasinformation
Theontologicalfoundationoftheinformationalinterpretationisadoublereification:
1. ofgeneticinformationasanon-physicalentity(Williams1966,1992).
2. ofinformationalspecificityasanon-physicalformofspecificity;
Informationalspecificityisontologicallydifferentfrombiochemicalspecificity.Crick’sinformationalspecificitywasreifiedasapeculiarkindofrelationshipbetweenDNAsequenceanddevelopmentaloutcome:
“Thespecificityofthegene-geneproduct(nucleicacidorprotein)relationshipwasinformationalandthusdifferentfromspecificityateveryotherlevelofbiologicalorganization,whichremainedphysical(orstereospecific).”(Sarkar2005,p.367)
3.5Themoleculargeneasinformation
Conformasonalcomplementarityofenzymesandsubstrateisaphysicalrelasonship,butthatofDNAwithitsgene-products(RNAtranscriptsandproteins)ispurely
informasonal.Whatdoesthismean?
3.6Molecularbiologyvsinformationtalk
Maindrawbackisthecreationoftwosuspiciousasymmetries:
1. betweenprocessesliketranscription,translationandproteinfoldingthatcanberepresentedininformationaltermsontheonehand,andallotherdevelopmentalprocessesnotamenabletoastraightforwardinformationalrepresentation;
2. betweentheputativecausalroleofDNAandextragenomicdevelopmentalresourcesindevelopment.
Thefirstasymmetryisunjustifiedbecauseprocessesliketranscription,translationandproteinfoldingturnedouttobeextremelycomplexbiochemicalprocesses,nodifferentinkindfromallotherdevelopmentalones.
Knowledgeabouteukaryotictranslationrevolutionisedbythediscoveryofalternativesplicingin1977:
“Inthecaseoftheegg-layinghormoneofAplysia,totakejustoneexample,oneandthesamestretchofDNAgivesrisetoelevenproteinproductsinvolvedinthereproductivebehaviorofthissnail.”(Rheinberger,Müller-WilleandMeuniersection3)
Proteinfolding(basedonAnfinsen’s“dogma”:theprimarystructureoftheproteinisdeterminedbytheprotein'saminoacidsequence):discoveryoftheroleofchaperonesandfoldingcatalyistsintheprocess.
3.7Proteinbiosynthesis
3.8Proteinbiosynthesis
3.9Contrivancesofprokaryosctranscripson
3.10Proteinbiosynthesis
3.10Proteinbiosynthesis
4.1DNA’scausalroleindevelopment
Maindrawbackisthecreationoftwosuspiciousasymmetries:
1.betweenprocessesliketranscription,translationandproteinfoldingthatcanberepresentedininformationaltermsontheonehand,andallotherdevelopmentalprocessesnotamenabletoastraightforwardinformationalrepresentation;
2.betweentheputativecausalroleofDNAandextragenomicdevelopmentalresourcesindevelopment.
Genesdeterminephenotypicoutcomes(seealsoclass3ondevelopment).
Genespossessaqualitativelydifferentkindofspecificity.
4.2Dogenesdeterminephenotypicoutcomes?
ConradHalWaddingtonproposedaninterpretationofgeneactionthatwasdeterministicdespitethewell-knowncomplexityofthegenotype-environmentrelationship(rememberWoltereck’sexperimentswithdaphniain1909,slide3.10class2).
“…thefactorwhich,inthedevelopmentofvertebrates,decideswhichofthealternativemodesofdevelopmentshallbefollowedistheorganiser,or,morespecifically,theactivechemicalsubstanceoftheorganiserwhichhasbeencalledtheevocator.”(Waddington1939,p.S37)
Theevocator(amolecularagent)playsthecausalroleindevelopmentalprocessesby“deciding”whichdevelopmentalpathistaken.
4.3Dogenesdeterminephenotypicoutcomes?
RememberWaddington’sepigeneticlandscape(slide3.4class2):
1. developmentisaprocessthatcanberepresentedasconsistingofmanydiscretestepsorbifurcationswithnointermediatesbetweenthem;
2. evocators“decide”whichpathistakenbythedevelopingorganismateverybifurcation;
3. inthissense,evocatorsaredeterminantsofdevelopment.
4.4Dogenesdeterminephenotypicoutcomes?
Waddington’sinference:genesidentifiedwithevocators:
“…genes...actinawayformallylike...evocators,inthattheycontrolthechoiceofalternative.”(Waddington1939,p.S37)
Developmentalbiologybecomesthereforetheprovinceofdevelopmentalgenetics.
AsWaddingtonclaimedlater:
“…weknowthatgenesdeterminethespecificnatureofmanychemicalsubstances,celltypes,andorganconfigurations;andwehaveeveryreasontobelievethattheyultimatelycontrolallofthem.”(Waddington1962,p.4)
TheideathatDNAisadevelopmentaldeterminantfinallyfounditsconceptualunderpinning.
(Cf.Sarkar2005+Vecchi2019).
4.5Theswitch-pointmodelofdevelopment
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4.6Genetic“determination”
Giventhattherecannotbeentiredevelopmentaltrajectoriesthataretotallygeneticallyorenvironmentallydetermined,theuseofthelanguageofdeterminationismisleading(West-Eberhard,2003,p.99-100).Thisissufficienttodispelthetraditionalideaofgeneticdetermination(i.e.,thatanadultphenotypeisfullydeterminedbygenomicinputs;cf.genexforphenotypePidea).
Butisthedevelopmentaloutcomebesidescompatiblewiththismodel?
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4.7Developmentalstructuralism
Sometimesgenesseemtodeterminedevelopmentaloutcomes.However,thisviewisnotincompatiblewithotherdevelopmentalapproachesthatconsidergenesassecondary,andsometimesirrelevantindevelopment.
Developmentalstructuralismisonesuchapproach:
“Byfocusingontheelasticandviscousfeaturesofthecytoskeleton,andneglectingtheextremelysmallaccelerations,theseauthorssucceededinprovingthatthecontractionofasinglecellpropagatestotheadjacentcellsandgeneratesaninvaginationintheepithelium.Suchmodelsarephilosophicallyinteresting…becausetheyhelptodispensewithpreformationistmyths:"[...]oncetriggered,themorphogeneticprocessofinvaginationproceedsonitsown,directedsolelybytheglobalbalanceofmechanicalforcesgeneratedlocallybyeachcell,andwithnorequirementforindividuallypreprogrammedsequencesofpatternsofcellshapechange"(Odelletal.1981,p.450).MahnerandBungep.298
4.8Developmentalconstructivism
Developmentalconstructivismendorsesthe“causalparity”thesis:
“….nocausalordeterminativepriorityindevelopmentcanbeassignedeithertothegenes,i.e.,tointernalfactors,ortotheenvironment,i.e.,toexternalfactors.Itisemphasizedthat"phenotypes"arenottransmittedfromonegenerationtothenext,e.g.,incodedforminthegeneticmaterial,butthattheyareconstructedanewineachgenerationthroughorganism-environmentinteractionsduringdevelopment.”MahnerandBungep.299
“Theconstructionistviewofdevelopmentalsocallsforanexpandednotionofinheritance(Oyama1985).Ifphenotypictraitsarenotinanywaytransmittedbutconstructedanewduringdevelopment,thenthequestionariseswhat,ifanything,doorganismsinherit.Ofcourse,organismsinheritgenes,buttheyalsoinheritcytoplasmicfactors(actuallytheentireinitialorganizationofthecell)and,afterall,acertainenvironment(Gray1992).”MahnerandBungep.300
Epigeneticinheritance
4.9Dogenespossessaqualitativelydifferentkindofspecificity?
TheargumentisfrequentlymadethatDNAisahighlyspecificdevelopmentalcause.
But,aspecificphenotypicchangecanbeproducedeitherthroughamutationorthroughachangeintheconcentrationofageneproductcausedbyenvironmentalfactors.Thesetwokindsofchangesarebiochemicallyequivalent(ZuckerkandlandVillet1988).
4.10DNAasapeculiarresource
ContemporarygenomicsandmolecularbiologymakeclearthatknowledgeofDNAsequenceisinsufficienttopredictaccuratelyproteinstructureand–evenmoreso-anyhigherlevelphenotypicoutcome(eventhoughexceptionsexist,e.g.,eyelessgene).
DNAisadevelopmentalresource,notadeterminant(Sarkar2005).
Givenallthis,canwestilldefendtheideathatDNAhasacentralroleindevelopment?Orshouldtheso-called“paritythesis”beendorsed?
Backin1926,HermannJosephMullerexplainedthecentralityofgenesinthismanner:
"…inallprobabilityallspecific,generic,andphyleticdifferences,ofeveryorder,betweenthehighestandlowestorganisms,themostdiversemetaphytaandmetazoa,areultimatelyreferabletochangesin...genes.”(Muller1962,p.195)
Thepeculiarityofthisclaimliesinthefactthatitwasmadein1926.Backthen,nobodyknewwhatgenesaremadeofandnobodyhadaclueabouthowcontrivedtherelationshipbetweengenesandphenotypeis.ButMullerwashypothesizingthatphenotypiccomplexityisdependentongeneticcomplexity.Washeright?
4.11DNAasapeculiarresource
Summingup
Thecomplexhistoryofgeneticsispavedwithmanyexperimentalandtheoreticaladvances:fromtheemergenceoftheMendelianparadigmofinheritancetothegenotype-conceptionofheredity,fromthemolecularizationofthegenetotheadvancesofcomparativegenomics.
Theclaimthatgenesareinformationismetaphorical:thecausalroleofgenescannotbeuncoveredwithoutabiochemicalunderstandingofgeneexpression.
Genesarenotdevelopmentaldeterminantsbuttheyarehighlyspecificcausesnotonaparwithotherdevelopmentalones.
Thecausalroleofgenesinevolutionhasyettobeunderstood:ifphenome(i.e.,thesetofphenolypesanorganismcanmanifest)complexitydependsongenome(i.e.,thesetofgenomicresourcesanorganismpossesses)complexity,thengenesarecentralinevolution.
Toclaimthatgene-basedmodelsofdevelopmentandevolutionmighteventuallydisappearbecausethegenemightnotturnouttobeaprimitiveontologicalcategoryofbiology(endofRheinberger,Müller-WilleandMeunieressay)isinmypersonalopinionaveryquestionableconclusion.
CLASS5-23March:EVOLUTION1.Vecchi,D.(2018).Biodiversiade:Oqueéeporqueéimportante.Chapter2.(IwillsendalsotheEnglishversion)
2.Sober:chapter1
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