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Biology - Week 3 Notes

Biology - Week 3 Notes - Biology 2108 – Summer 2008 –...

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Unformatted text preview: Biology 2108 – Summer 2008 – Dr. Davis Abbreviated lecture notes from the week starting 6/9/08 Corresponds with Chapters 25-26 in Campbell (7th Edition) 25 - Phylogeny and Systematics Investigating the Tree of Life • Phylogeny- The evolutionary history of a species or group of related species • To uncover phylogenies, biologists use systematics … • Systematics- an analytical approach to understanding the relationships of organisms, both present-day and extinct Systematics makes use of many types of data! • Fossil, morphological, biochemical, and molecular comparisons can all be used to infer evolutionary relationships • Well supported phylogenies are based on common ancestries inferred from multiple lines of evidence! The Fossil Record • Is a substantial, but incomplete record of evolutionary change • Biased in favor of organisms that existed for longer periods of time, were abundant and wide-spread, and possessed hard parts that were likely to fossilize • Can reveal ancestral characteristics that may have been lost over time • Inform us of the order of appearance of new characteristics Morphological and Molecular Homologies • Phylogenetic history can be inferred from morphological and molecular similarities among living organisms • Organisms that share very similar morphologies or similar DNA sequences are likely to be more closely related than organisms with vastly different structures or sequences. However… we have to be careful in our choice of characters!!! Sorting Homology from Analogy • Homologies are similarities due to shared ancestry… these are useful for building a phylogeny! • Analogies ( Homoplasies ) are similarities due to convergent evolution rather than shared ancestry… these can lead to an incorrect phylogenetic hypothesis!!! Convergent Evolution • Not all similar traits are homologous • Convergent evolution- the independent evolution of similar structures or functions in unrelated groups • Convergent evolution occurs when similar environmental pressures and natural selection lead to the production of similar ( analogous ) adaptations in organisms from different evolutionary lineages • Analogous structures or molecular sequences that evolved independently are also called homoplasies We have to be very careful to distinguish homologies from homoplasies ( analogies )! Evaluating Molecular Homologies Systematics involves the use of computer programs and mathematical tools when analyzing comparable DNA segments from different organisms • Problematic similarities are present at the molecular level too • Reversals (or back-mutations) occur when a mutated base is hit with a second mutation back to the ancestral base (Example given in lecture, textbook) Classification and Phylogeny • 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 –...
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Biology - Week 3 Notes - Biology 2108 – Summer 2008 –...

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