Ch 26 supplement

Ch 26 supplement - Chapter26...

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Unformatted text preview: Chapter26 PhylogenyandtheTreeofLife Overview:InvestigatingtheTreeofLife Leglesslizardshaveevolvedindependentlyinseveraldifferentgroups So,WhatisPhylogeny? Phylogenyistheevolutionaryhistoryofaspeciesorgroupofrelatedspecies Thedisciplineofsystematicsclassifiesorganismsanddeterminestheirevolutionaryrelationships Systematistsusefossil,molecular,andgeneticdatatoinferevolutionaryrelationships Figure26.2Anunexpectedfamilytree. Concept26.1:Phylogeniesshowevolutionaryrelationships Taxonomyistheordereddivisionandnamingoforganisms  BinomialNomenclature Inthe18thcentury,CarolusLinnaeuspublishedasystemoftaxonomybasedonresemblances Twokeyfeaturesofhissystemremainusefultoday:two ­partnamesforspeciesandhierarchicalclassification Thetwo ­partscientificnameofaspeciesiscalledabinomial Thefirstpartofthenameisthegenus Thesecondpart,calledthespecificepithet,isuniqueforeachspecieswithinthegenus ThefirstletterofthegenusisCAPITALIZED,andtheentirespeciesnameisitalicized Bothpartstogethernamethespecies(notthespecificepithetalone) HierarchicalClassification Linnaeusintroducedasystemforgroupingspeciesinincreasinglybroadcategories Thetaxonomicgroupsfrombroadtonarrowaredomain,kingdom,phylum,class,order,family,genus,and species Ataxonomicunitatanylevelofhierarchyiscalledataxon Thebroadertaxaarenotcomparablebetweenlineages Forexample,anorderofsnailshaslessgeneticdiversitythananorderofmammals Figure26.3Linnaeanclassification  LinkingClassificationandPhylogeny Systematistsdepictevolutionaryrelationshipsinbranchingphylogenetictrees Figure26.4Theconnectionbetweenclassificationandphylogeny. Linnaeanclassificationandphylogenycandifferfromeachother SystematistshaveproposedthePhyloCode,whichrecognizesonlygroupsthatincludeacommonancestorand allitsdescendants  Aphylogenetictreerepresentsahypothesisaboutevolutionaryrelationships Eachbranchpointrepresentsthedivergenceoftwospecies Sistertaxaaregroupsthatshareanimmediatecommonancestor Arootedtreeincludesabranchtorepresentthelastcommonancestorofalltaxainthetree Abasaltaxondivergesearlyinthehistoryofagroupandoriginatesnearthecommonancestorofthegroup Apolytomyisabranchfromwhichmorethantwogroupsemerge Figure26.5Howtoreadaphylogenetictree.  WhatWeCanandCannotLearnfromPhylogeneticTrees Phylogenetictreesshowpatternsofdescent,notphenotypicsimilarity Phylogenetictreesdonotindicatewhenspeciesevolvedorhowmuchchangeoccurredinalineage Itshouldnotbeassumedthatataxonevolvedfromthetaxonnexttoit ApplyingPhylogenies Phylogenyprovidesimportantinformationaboutsimilarcharacteristicsincloselyrelatedspecies Aphylogenywasusedtoidentifyt  Figure26.6Inquiry:Whatisthespeciesidentityoffoodbeingsoldaswhalemeat?  Concept26.2:Phylogeniesareinferredfrommorphologicalandmoleculardata Toinferphylogenies,systematistsgatherinformationaboutmorphologies,genes,andbiochemistryofliving organisms MorphologicalandMolecularHomologies Phenotypicandgeneticsimilaritiesduetosharedancestryarecalledhomologies OrganismswithsimilarmorphologiesorDNAsequencesarelikelytobemorecloselyrelatedthanorganisms withdifferentstructuresorsequences SortingHomologyfromAnalogy Whenconstructingaphylogeny,systematistsneedtodistinguishwhetherasimilarityistheresultofhomology oranalogy Homologyissimilarityduetosharedancestry Analogyissimilarityduetoconvergentevolution Convergentevolutionoccurswhensimilarenvironmentalpressuresandnaturalselectionproducesimilar (analogous)adaptationsinorganismsfromdifferentevolutionarylineages Figure26.7Convergentevolutionofanalogousburrowingcharacteristics. Batandbirdwingsarehomologousasforelimbs,butanalogousasfunctionalwings Analogousstructuresormolecularsequencesthatevolvedindependentlyarealsocalledhomoplasies Homologycanbedistinguishedfromanalogybycomparingfossilevidenceandthedegreeofcomplexity Themorecomplextwosimilarstructuresare,themorelikelyitisthattheyarehomologous Figure26.8AligningsegmentsofDNA. Figure26.9Amolecularhomoplasy. Itisalsoimportanttodistinguishhomologyfromanalogyinmolecularsimilarities Mathematicaltoolshelptoidentifymolecularhomoplasies,orcoincidences MolecularsystematicsusesDNAandothermoleculardatatodetermineevolutionaryrelationships  Concept26.3:Sharedcharactersareusedtoconstructphylogenetictrees Oncehomologouscharactershavebeenidentified,theycanbeusedtoinferaphylogeny  Cladistics Cladisticsgroupsorganismsbycommondescent Acladeisagroupofspeciesthatincludesanancestralspeciesandallitsdescendants Cladescanbenestedinlargerclades,butnotallgroupingsoforganismsqualifyasclades Avalidcladeismonophyletic,signifyingthatitconsistsoftheancestorspeciesandallitsdescendants Aparaphyleticgroupingconsistsofanancestralspeciesandsome,butnotall,ofthedescendants Apolyphyleticgroupingconsistsofvariousspecieswithdifferentancestors Figure26.10Monophyletic,paraphyletic,andpolyphyleticgroups  SharedAncestralandSharedDerivedCharacters Incomparisonwithitsancestor,anorganismhasbothsharedanddifferentcharacteristics Asharedancestralcharacterisacharacterthatoriginatedinanancestorofthetaxon(Theyaresharedwith otherorganismsindifferentclades) Asharedderivedcharacterorsynapomorphyisanevolutionarynoveltyuniquetoaparticularclade Acharactercanbebothancestralandderived,dependingonthecontext Figure26.11Constructingaphylogenetictree. Anoutgroupisaspeciesorgroupofspeciesthatiscloselyrelatedtotheingroup,thevariousspeciesbeing studied Theoutgroupisagroupthathasdivergedbeforetheingroup Systematistscompareeachingroupspecieswiththeoutgrouptodifferentiatebetweensharedderivedand sharedancestralcharacteristics Characterssharedbytheoutgroupandingroupareancestralcharactersthatpredatethedivergenceofboth groupsfromacommonancestor  PhylogeneticTreeswithProportionalBranchLengths  Insometrees,thelengthofabranchcanreflectthenumber ofgeneticchangesthathavetakenplaceinaparticularDNA sequenceinthatlineage Inothertrees,branchlengthcanrepresentchronologicaltime,andbranchingpointscanbedeterminedfrom thefossilrecord  MaximumParsimonyandMaximumLikelihood Systematistscanneverbesureoffindingthebesttreeinalargedataset Theynarrowpossibilitiesbyapplyingtheprinciplesofmaximumparsimonyandmaximumlikelihood MaximumParsimonyandMaximumLikelihood Maximumparsimonyassumesthatthetreethatrequiresthefewestevolutionaryevents(appearancesof sharedderivedcharacters)isthemostlikely Theprincipleofmaximumlikelihoodstatesthat,givencertainrulesabouthowDNAchangesovertime,atree canbefoundthatreflectsthemostlikelysequenceofevolutionaryevents  PhylogeneticTreesasHypotheses Thebesthypothesesforphylogenetictreesfitthemostdata:morphological,molecular,andfossil Phylogeneticbracketingallowsustopredictfeaturesofanancestorfromfeaturesofitsdescendents Forexample,phylogeneticbracketingallowsustoinfercharacteristicsofdinosaurs Figure26.16Aphylogenetictreeofbirdsandtheircloserelatives. Birdsandcrocodilesshareseveralfeatures:four ­chamberedhearts,song,nestbuilding,andbrooding Thesecharacteristicslikelyevolvedinacommonancestorandweresharedbyallofitsdescendants,including dinosaurs Thefossilrecordsupportsnestbuildingandbroodingindinosaurs Figure26.16Aphylogenetictreeofbirdsandtheircloserelatives.   Comparingnucleicacidsorothermoleculestoinferrelatednessisavaluableapproachfortracingorgan evolutionaryhistory DNAthatcodesforrRNAchangesrelativelyslowlyandisusefulforinvestigatingbranchingpointshundredsof millionsofyearsago mtDNAevolvesrapidlyandcanbeusedtoexplorerecentevolutionaryevents GeneDuplicationsandGeneFamilies Geneduplicationincreasesthenumberofgenesinthegenome,providingmoreopportunitiesforevolutionary changes Repeatedgeneduplicationsresultingenefamilies Likehomologousgenes,duplicatedgenescanbetracedtoacommonancestor  Concept26.6:Newinformationcontinuestoreviseourunderstandingofthetreeoflife Recently,wehavegainedinsightintotheverydeepestbranchesofthetreeoflifethroughmolecular systematics  FromTwoKingdomstoThreeDomains Earlytaxonomistsclassifiedallspeciesaseitherplantsoranimals Later,fivekingdomswererecognized:Monera(prokaryotes),Protista,Plantae,Fungi,andAnimalia Morerecently,thethree ­domainsystemhasbeenadopted:Bacteria,Archaea,andEukarya Thethree ­domainsystemissupportedbydatafrommanysequencedgenomes Figure26.21Thethreedomainsoflife.  ASimpleTreeofAllLife Thetreeoflifesuggeststhateukaryotesandarchaeaaremorecloselyrelatedtoeachotherthantobacteria ThetreeoflifeisbasedlargelyonrRNAgenes,asthesehaveevolvedslowly Therehavebeensubstantialinterchangesofgenesbetweenorganismsindifferentdomains Horizontalgenetransferisthemovementofgenesfromonegenometoanother Horizontalgenetransferoccursbyexchangeoftransposableelementsandplasmids,viralinfection,andfusion oforganisms Horizontalgenetransfercomplicateseffortstobuildatreeoflife Figure26.22Theroleofhorizontalgenetransferinthehistoryoflife. ...
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This note was uploaded on 12/04/2011 for the course BIO 200 taught by Professor Ejiofor during the Fall '11 term at TN State.

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