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Unformatted text preview: 1 Phylogenetics and Systematics How to read phylogenetic trees Classification (Systematics) Types of phylogenetic trees How to make phylogenetic trees How to use phylogenetic trees The fossil record provides information about the history and relationships among organisms 100 million year old dragonfly fossil The fossil record Is based on the sequence in which fossils have accumulated in such strata Fossils reveal Ancestral characteristics that may have been lost over time Fossils dates Provide minimum estimates of the age of a taxon 2 But the history of organisms is also written in their features, and in their genes. Biologists use morphological, biochemical, and molecular comparisons to infer evolutionary relationships. Molecular (sequence) data are now the dominant data source. This is a cladogram. One type of phylogenetic tree. Are you more closely related to a fungus or a plant? Is a tulip more closely related to a mushroom or a human? 3 How to read a phylogenetic tree Morphological and Molecular Homologies In general, organisms that share very similar morphologies or similar DNA sequences are likely to be more closely related. Homology vs. Analogy A potential source of error in reconstructing relationships is similarity due to convergent evolution, called analogy, rather than shared ancestry. Homologous features held in common by a group due to shared ancestry Analogous features are due to convergent evolution 4 Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages Marsupial mole Mole (placental) (The two animals above are exactly as closely related to one another as the two animals below) Human Kangaroo These wings are analagous Bat Bird Each bone is homologous 5 To determine whether a character state is homologous or analagous One needs to look at many characters Lizard Four-chambered heart Bird Mammal Lizard Four-chambered heart Bird Mammal Four-chambered heart (a) Mammal-bird clade (b) Lizard-bird clade Analogous (convergent) structures or molecular sequences that evolved independently Are also called homoplasies Molecular Homologies Systematists use computer programs and mathematical tools to align comparable DNA segments from different organisms Deletion Insertion 6 Here are two unrelated DNA sequences They happen to share 25% of their sites Computer programs are used to separate these chance homoplasies, from similarities that imply relationships A C G G A T A G T C C A C T A G G C A C T A T C A C C G A C A G G T C T T T G A C T A G Figure 26.9 Phylogenetic systematics connects classification with evolutionary history Taxonomy Is the ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences Binomial Nomenclature Binomial nomenclature...
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page - 1 Phylogenetics and Systematics How to read...

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