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Phylogenetic Trees Phylogenetic Trees and Cladograms • What are they? • Graphical representations (models) of evolutionary history ▫ They show how species of the past are related to other species ▫ Show relations that can be tested • What does phylogeny mean? ▫ Phylogeny: Tracing the origin of a species based on evolutionary relationships Geology and the fossil record • Fossils help us produce phylogenetic trees based on morphological characteristics Classification of living things • Classical taxonomy was invented by Carolus Linnaeus ▫ All classification done by physical characteristics ▫ Linnaeus invented binomial nomenclature Two names that describe a species Homo sapiens Drosophila melanogaster Canis familiarus Mus musculus Linnaeus • He also created hierarchical groups of classification • Grouping organisms that seem to be related by physical characteristics ▫ ▫ ▫ ▫ ▫ ▫ ▫ ▫ Domain Kingdom Phylum Class Order Family Genus Species Phylogenetic trees help us classify living things • Modern classification involves using phylogentic trees ▫ Based on evidence from Genetics Morphology Development Biochemistry Fossils (reveal traits that have been lost) • The goal is to find how species are evolutionarily related ▫ More in common = less likely they evolved independently Classification and phylogeny are linked! • Why does classical taxonomy overlap with today’s phylogenetic trees? • Because animals that are evolutionarily related share physical characteristics Stop Here! • Bring your questions for class tomorrow! Phylogenetic trees and cladograms • A cladogram is like a phylogenetic tree • Both show that the relatedness of any two groups by how recently the groups have had shared a common ancestor • How are they different? ▫ Phylogenetics is the general idea of making trees that show evolutionary relationships ▫ Cladistics creates cladograms based on shared derived characteristics Phylogenetic trees and cladograms • What is a shared derived characteristic? ▫ A trait that every individual has as you move forward in the diagram Claws and nails are shared derived characteristics in this example for lizard, pigeon, mouse and chimp • Example of a phylogeny • Made with computer DNA sequencing • Show evolutionary relationships • Example of a cladogram ▫ Shows shared derived characteristics Clade: ancestral species and all of its descendants Making a phylogenetic tree • Based on evidence from ▫ Genetics, Morphology, Development, Biochemistry, Fossils etc. ▫ Systematics: the process of analyzing this data to understand species diversity and relationships DNA is particularly helpful • Morphological and molecular ▫ Homology vs. analogy ▫ Divergent vs. convergent • Molecular homologies ▫ DNA sequences ▫ Proteins ▫ What challenges can be anticipated with these molecules? Making a cladogram • Look for homologous characteristics ▫ Physical or Molecular DNA, Proteins • Shared primitive characters – common to all members of the group ▫ Backbone • Shared derived characters – found only in group of interest ▫ Mammals and hair Be careful! • These things can make it seem like you have a relationship but they can be misleading • Morphological homologies ▫ Homology vs. analogy ▫ Divergent vs. convergent • Molecular homologies ▫ DNA sequences ▫ Proteins Outgroup • Species that is less closely related to the entire group, than any of the individual member are to the to other members of the group Practice Time • Construct a cladogram using 4 animals that you know yourself • Include shared derived characteristics and one primitive characteristic Practice time • Make a cladogram with the following animals: • Identify the shared derived characteristics as well as one shared primitive characteristic ▫ ▫ ▫ ▫ ▫ ▫ ▫ ▫ Rabbit Shark Bird Alligator Chimpanzee Frog Trout One of many possible answers One more • Make a cladogram with the following animals: • Identify the shared derived characteristics as well as one shared primitive characteristic • Identify the outgroup ▫ ▫ ▫ ▫ ▫ ▫ Rat Raccoon Guinea Pig Beaver Mouse Rabbit 28. (A) Based on the data in the table below, draw a phylogenetic tree that reflects the evolutionary relationships of the organisms based on the differences in their cytochrome c amino-acid sequences. Based on the data, identify which organism is most closely related to the chicken and explain your choice. THE NUMBER OF AMINO ACID DIFFERENCES IN CYTOCHROME c AMONG VARIOUS ORGANISMS Horse Horse Donkey Chicken Penguin Snake Donkey Chicken Penguin Snake 0 1 11 13 21 0 10 12 20 0 3 18 0 17 0 Cladograms and phylogenetic trees are a work in progress • Constantly being revised based on new data • Scientists like to fight