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DPTopic5.4: Cladistics EssentialIdea:Theancestryofgroupsofspeciescanbededucedby comparingtheirbaseoraminoacidsequences Clades&Cladograms U1: A clade is a group of organisms that have evolved from a common ancestor U5: Cladograms are tree diagrams that show the most probable sequence of divergence in clades. A1: Cladograms including humans and other primates. S1: Analysis of cladograms to deduce evolutionary relationships. Cladesincludeallthespeciesthatarestillaliveandalsothosethatareextinct. Exercise1:Whatevolutionaryrelationshipsareindicatedbythiscladogram? MarkthecommonancestorforthechimpanzeeandtheHuman. Exercise2:Workthroughtheseinstructions Constructing Cladograms Eukaryotic Multicellular Vertebral Column Amniote egg Hair Placenta Opposable Thumbs Totals Paramecium Flatworm Shark Eagle Koala Camel Human To make a cladogram (the first step has been done for you): 1. Make a list of organisms to be included 2. List as many as possible characteristics which each organism possesses, biochemical or morphological - tick the boxes for each organism 3. Decide on the primitive characteristic (this is the one that all organisms share) 4. Construct a cladogram with the first branch being the organism with the fewest derived characteristics Remember - Primitive characteristics are those that have the same structure and function and evolved early on in the organisms being studied. Derived traits are those that have the same structure and function but evolved later as a modification to a previous trait The original line at the base is the common ancestors lineage Using Biochemical Evidence U2: U3: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein. Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. Exercise 3: Using biochemical variation to deduce evolutionary relationships, and the molecular clock 1. A A A A A T T T C C C C G G G G A A A A T T T T C C C C G G A A T 2. A T A A A T T T C C C C G G A G A A A A T T T T C C C C G G A A T 3. A A A A C T T T C C C C G G A G A A A A T T T C C C C C G G G A C 4. T A T A C T T T C C C T G G A G A A A A T A T T C C G C G G G A C Each sequence of bases above has been taken from the same section of highly conserved DNA from four different mammals. Taxonomists want to use them to resolve the phylogeny of these species. To help them you need to work through the following exercise. 1. 2. 3. 4. 5. 6. How many differences are there in the sequences between each species (Use the matrix on the next page)? Which species do you think are most closely related based on the sequences above? Why? Transcribe and Translate the sequences and answer the above questions using the sequence of amino acids. From your investigation evaluate the effectiveness of using biochemical variations to deduce phylogenies Evaluate how effective these different sequences would be as a molecular or evolutionary clock. Using the differences within these tables create your own cladogram. Amino acid sequence number 1 1 2 3 4 2 3 4 x x x x Amino Acid Sequence number Amino Acid Sequence number DNA sequence number 1 1 2 3 4 2 3 4 x x x x Analogous&HomologousTraits U4: • • Traits can be analogous or homologous. Homologousstructuresarethosebasedonthesameplanbutmaybeadaptedfordifferent purposes E.g.bat’swing,humanarmandsealflipperareallmodificationsofthesamebasicplan (divergentevolution) • Thissimilarityinformindicatesacommonancestor,andcanbeusedtocreateanaturalor phylogeneticclassification • Analogousstructuresarethosethatresembleeachotherinfunctionbutdifferintheir fundamentalstructure(convergentevolution) • E.g.bat’swingandinsectwing,squidandvertebrateeyes • Classificationbasedonanalogousstructuresresultsinanartificialclassification ConstructingCladograms • • • • Cladogramscanbeconstructedusingmorphologicalorbiochemicalevidence Ifusingmorphologytaxonomiststendtouse“primitive”characteristics,oneslikelytohave beensharedbyacommonancestortoworkoutthephylogeneticrelationship Taxonomistsmustbecarefultobuildcladogramsbasedonhomologousstructures Biochemicalevidence(immunologicalstudies)canalsobeusedtocreatecladograms. Combinedwithmorphologicaldatathesestudiestendtogiveamorereliablephylogeny Exercise4: ReclassificationoftheFigworts U6: Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species. A2: Reclassification of the figwort family using evidence from cladistics. Essential idea: The ancestry of groups of species can be deduced by comparing their base or amino acid sequences. Biology guide 5.4 Cladistics Nature of science: Falsification of theories with one theory being superseded by another—plant families have been reclassified as a result of evidence from cladistics. (1.9) Understandings: Theory of knowledge: t A clade is a group of organisms that have evolved from a common ancestor. t t Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein. t Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. t Traits can be analogous or homologous. t Cladograms are tree diagrams that show the most probable sequence of divergence in clades. t Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species. t Application: Cladograms including humans and other primates. t Application: Reclassification of the figwort family using evidence from cladistics. t Skill: Analysis of cladograms to deduce evolutionary relationships. 71 Topic 5: Evolution and biodiversity Applications and skills: A major step forward in the study of bacteria was the recognition in 1977 by Carl Woese that Archaea have a separate line of evolutionary descent from bacteria. Famous scientists, including Luria and Mayr, objected to his division of the prokaryotes. To what extent is conservatism in science desirable?