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Lecture 17

Biology Lecture 17.docx

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Biology 1001A
Tom Haffie

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Biology Lecture 17: Phylogeny  Speciation is Reversible: o Speciation can be reversed, if we can go back to the formation of a hybrid swarm. This can occur if the isolating mechanisms breakdown.  Phylogeny: o Phylogeny: an attempt to reconstruct the evolutionary history of all life on earth o We know that all life on earth came from one common ancestor, however different species had more recent common ancestors than others  Homology vs. Homoplasy: o Homology: similarity due to a recent common ancestor o Homoplasy: not all similarity reflects common ancestory  misleading similarity (convergence): two species do not have a common recent ancestor, but they appear similar because they share the same habitat  misleading dissimilarity (divergence): two species are closely related, but since they inhabit different environments or have different selection pressures they do not appear to be similar  Homology vs. Homoplasy: o Homologous traits: lead you to uncover the true phylogeny o Homoplasious traits: mislead you to the wrong phylogeny o To determine whether traits are homologous or homoplasious , you can use cladistic analysis. o In cladisitic analysis, only shared and derived traits (synapomorphies) are informative  Synapomorphies: o Traits common or shared among two or more groups o Presumably, these traits are similar due to homology b
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