Bio1B Evolution 2 The Darwin Wallace principle of Natural selection Last lecture Introduction to Craig lecture outline Foundations Pre Darwinian background Darwin early influences Beagle voyage Wallace Individuals within a population vary for one or more characteristics traits Traits are to some extent inherited by offspring from their parents More offspring are produced than can survive those with traits that improve survival reproduction leave more offspring these favorable traits will accumulate in the population over generations Today Natural selection principles lines of evidence in the Origin Descent with modification Estimation interpretation of phylogeny Some major insights about the Tree of Life 3 kingdoms Archaea Bacteria Eukarya Assembling the eukaryote cell Metazoan origins relationships On line resources Understanding Evolution UCMP http evolution berkeley edu Tree of life www tolweb org tree 1 Lines of evidence in the Origin of the species by means of natural selection Darwin 1859 Artificial selection as analogy to natural selection Biogeography Nested geographic distributions Homology of traits modified for different purposes Population pressure 2 Homologous structures variations on a structure present in a common ancestor Fig 22 10 Fig 22 17 3 Human Cat Whale Bat Fig 22 18 Molecular homologies new insights invisible to Darwin Anatomical homologies of embryos Pharyngeal pouches Genetic code Transcription translation machinery Colinear segmentation Hox genes etc etc Post anal tail Human embryo Chick embryo Fish gills Pharangeal pouches Mammals ears throat 6 Descent with modification by natural selection extinction The current view of the phylogenetic hierarchy cf Aristotle s scala naturae time Understanding Evolution web site Phenotype 7 8 What evidence do we use to estimate the tree of life morphology fossils Molecules DNA extant Key concepts in tree thinking J and K are sister taxa General principles Taxa species genera etc are grouped by shared derived traits Taxa should be monophyletic 9 Examples of shared derived traits that group major lineages of vertebrates c Monophyletic clade b c a b B is most recent common ancestor to D E G H From Figs 26 5 26 10 a b c character states for a trait c is a shared derived state for D E b is a sharedancestral state for D E c is analogous not homologous DNA sequence variation Fitting observed patterns of sequence variation at homologous aligned sites to a phylogenetic hypothesis see also Fig 26 8 Fig 26 11 10 Parsimony minimize changes on tree Maximum likelihood Bayesian data model of sequence evolution Find tree that is most probable given the data Mushroom Tulip 0 30 40 0 40 Human Mushroom Tulip 0 Percentage differences between sequences 25 15 15 20 15 10 5 John Huelsenbeck IB MVZ curator of trees Tree 1 More likely Comparison of possible trees 5 Estimating divergence times from a phylogeny Branch lengths are proportional to amount of change Fig 29 19 Molecular clock Zuckerkandle Pauling 1960s Some genes evolve at approx constant rate Absolute rate can be estimated from fossils at or near nodes This calibration can be used to estimate other divergence times in tree See text for caveats branch node Tree 2 Less likely Figs 26 12 26 13 Surprise 1 3 Domains of life 14 Cool stuff understanding metazoan origins Nicole King MCB Fig 26 21 Based initially on rRNA gene sequences 15 Hox genes Human Adhesion genes Methods for estimating phylogeny from molecular data See also Fig 32 3 16 Surprise 2 Eukaryotic cells were assemble via endosymbiosis mitochondrial chloroplasts are modified symbiotic bacteria Each has a small genome separate from the nucleus 17
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