ZOOL 4133: phylogenetics
23 Cards in this Set
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most closely related taxa, should have most traits in common
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logic of phylogenetic inference
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homologous traits that are shared among species and are similar because they were modified in a common ancestor (shared derived traits)
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synapomorphies
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examples of synapomorphies
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1. Fur, even though being a homologous trait, it is not a syapomorphy because it is not derived
2. bobcat tail IS a syapomorphy characterizing bobcats and lynxes
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these traits identify monophyletic groups
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synapomorphies
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identification of derived requires ......
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outgroup analysis
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bacterial examples for synapomorphies
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1. DNA, even though being a homologous trait, is not a synapomorphy because it is not derived
2. cell structure is a synapomorphy characterizing bacteria and eukaryotes
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The most closely related taxa should have most traits in common!
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Logic of phylogenetic inference
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Two key insights to the logic of phylogenies..
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1. Synapomorhies identify evolutionary branch points
2. Synapomorphies are nested
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occurs when natural selection favors similar structures as solutions to problems posed by similar environments (analogous traits)
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Convergent evolution
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Leads to trait similarity, but traits are not homologous
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Convergent Evolution
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"back mutations" that can remove synapomorphies
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Reversals
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Both lumped under homoplasy
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convergent evolution
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can reverse a DNA sequence back to the same as the original ancestor
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reversal
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difference btw synapomorphies and homoplasies
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Synaps maximize the use of reliable info and homoplasies minimize the impact of misleading info.
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use the most simple explanation available
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parsimony
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similarity in the characters found in different species that is due to convergence, parallelism, or reversal ( not common descent)
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homoplasy
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the similarity between species that result from inheritance of traits from a common ancestor
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Homology
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criterion for selecting among alternative patterns or explanations based on minimizing the total amount of change or complexity
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parsimony
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Morphology describe pros and cons
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1. essential when only fossils are available
2. powerful when homology can be distinguished from homoplasy
3. Data is hard to collect
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Molecules describe the pros and cons of using it for phylogenetics
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1. data relatively easy to collect
2. homoplasies can statistically be accounted for
3. entirely avoiding homoplasies is almost impossible
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the pros of phylogeny and systematics
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High predictability and explanatory power.
classification based on relationships rather than morphological similarities
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example used to describe molecular clocks
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head/body lice in humans helped date when ppl started wearing clothes. they used the divergence tiime between head and body lice as an estimate of the origin of clothes.
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the use of evolutionary trees in answering questions about the geographic distribution of organisms.
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Phylogeography
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ZOOL 4133: phylogenetics