UW-Madison BOTANY 940 - Agreement Among Gene Trees Could Be Used as Evidence of Common Ancestry (33 pages)

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Agreement Among Gene Trees Could Be Used as Evidence of Common Ancestry



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Agreement Among Gene Trees Could Be Used as Evidence of Common Ancestry

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Pages:
33
School:
University of Wisconsin, Madison
Course:
Botany 940 - Seminar in Plant Systematics and Evolution
Seminar in Plant Systematics and Evolution Documents

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Agreement among gene trees could be used as evidence of common ancestry Jessica Clarke and Flor Rodriguez March 21st 2006 Arguments for common ancestry the genetic code is a frozen accident when life first arises it alters the environment so as to make subsequent start ups much less probable species with common ancestor are more likely to exhibit congruence in character state patterns than species that originated separately Hypothesis of common ancestry by Penny et al 1982 Prediction Orthologous genes should lead to similar trees because they are expected to share the same evolutionary history developed an algorithm that guaranteed to find all minimal length trees implemented a tree comparison metric to measure closeness calculated the expected distribution of this metric Conclusion Theory of evolution leads to quantitative predictions that are testable and falsifiable Measuring the difference T1 T11 complete data set T12 T17 T18 T19 T26 cytochrome c fibrinopeptide A fibrinopeptide B T27 T32 T33 T39 haemoglobin haemoglobin Measuring the difference The symmetric difference metric on two trees counts the number of edges that occur in one but not both trees Critic by Sober and Steel 2002 Common ancestry might be untestable Long ages of time might have erased the pertinent evidence I X Y ne 4rt n 1000 t 20 million years r 1 in 2million years No method can infer X from Y with a probability that is any better than simply ignoring Y and blindly guessing X I X Z 4k maxi nie 4rti n 100 t 20 million years r 1 in 100 million years K 10 000 No method can reliably determine from this data how these four groups are related historically Response from Penny et al 2003 Methods of tree construction based on parsimony assume common ancestry Methods other than parsimony can be used and should be favored if they give more consistent results when analyzing and comparing different data sets Response from Penny et al 2003 The hypothesis of common ancestry CA might be untestable Some



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