slatkin10Answers - Bio 1B, Spring, 2007, Evolution section...

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Bio 1B, Spring, 2007, Evolution section 1 of 4 Updated 3/16/07 3:07 PM Lecture 10 10 Phylogenetic systematics. Reading: 7 th edition 492-504; 6 th edition 492-502. The Linnaean system of classification is hierarchical Higher categories The major categories are domain. kingdom, phylum, class, order, family, genus, species. Intermediate categories exist, such as subphylum and superfamily. Phylogenetic tree (phylogeny) Darwin and classification In the Origin , Darwin said that descent from a common ancestral species could explain why the Linnaean system is hierarchical. Species in the same genus had a common ancestor more recently than species in different genera in the same family. The only figure in the Origin illustrated his idea. He introduced the idea of a phylogenetic tree. A phylogenetic tree represents the history of most groups of species For a phylogenetic tree to be a good description of the history of a group, the time it takes for new species to form (represented by the splitting of lineages) has to be very short compared to how long each species was present. The phylogeny of humans, chimps, gorillas and bonobos is typical and thought to be roughly accurate. A few groups of plants, such as those in the genus Clarkia , do not have a tree-like history because many species are allopolyploids. The history of Clarkia and other such groups is reticulate (net-like) in which some species have two ancestors. Information in a phylogenetic tree The pattern of branching indicates ancestry. The branch lengths indicate times. Cladogram A cladogram summarizes the branching pattern but contains no information about times. Be sure to understand the difference between a phylogenetic tree and a cladogram. A phylogenetic tree represents the pattern of evolution A tree is a convenient summary of what actually happened. If you could replay the webcast of life, you could discover the tree that describes the true history of a group of species. Phylogenetic trees and classification Darwin and taxonomy. Darwin did not address the practical problem of how to use evolutionary history to classify species into higher groups. The problem was then and is still that, although there is a phylogenetic tree that describes the history of most groups, it is difficult to know what the correct tree is.
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Bio 1B, Spring, 2007, Evolution section 2 of 4 Updated 3/16/07 3:07 PM Lecture 10 With the advent of DNA sequencing, much effort is going into inferring the
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slatkin10Answers - Bio 1B, Spring, 2007, Evolution section...

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