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lecture 4 BILD3

lecture 4 BILD3 - Lecture 4 Each Branch Point o Represents...

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Lecture 4 Each Branch Point o Represents the divergence of two lineages o Taxa more closely related on the phylogeny. o Cladograms Cladograms o Imply the relative order of divergences of taxa but provide no information about the amount of change, or the time-depth of various events Phylograms o In a phylogram The length of a branch in a phylogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage. Ultrametric Trees o The branching pattern is the same as in a phylogram, but all the brances that can be traced from the common ancestor to the present are of equal length. Branch lengths on an ultrametric tree represent a direct estimate of time. o How to read a phylogenetic tree Sister taxa- 2 taxa that derive from an immediate common ancestor, each other’s closest relative [(a) species A and B] Tree (b) same information as tree (a) Tree © different phylogeny from tree (a) Tree (d) and (e) show same information – different styles. A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants o Examples: mamalia, aves (birds), angiosperms, insects, etc. a para phyletic grouping consists of an ancestrial species and some, but not all, of the descendants examples: Traditionally defined Dinosauria, fish, gymnosperms polyphyletic grouping consists of various species that lack a common ancestor o examples: marine mammals, bipedal mammals, flying vertebrates, trees, etc. How to build a phylogenetic tree? o How do we infer evolutionary relationships? Measures as many traits as possible in the group of organisms External and internal morphology (skeleton), behavior, cell structure, chromosome #, nucleotide sequences in DNA, etc o Even character can have different character states Character:mode of reproduction States: ovipary, vivipary Whn character states all agree – building a tree is easy Example – human, chimpanzee, earthworm o All 3 share some traits Bilaterally symmetrical Multicellular
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Mobile Digestive track tube o Humans and chimps share a lot of characters that earthworm doesn’t Backbone 4 limbs Endoskeleton Lungs o Virtually no traits that Worms share with humans but not chijmps, or worms share with chimps but not humans o Birds bats and dogs which tree is right Birds and bats look a lot alive live alike But we know bats and dogs are mammals, share a more recent common ancestor than birds o Why do character states conflict?
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