Bio1AL_Sum09_lab8_cladistics

Bio1AL_Sum09_lab8_cladistics - Understanding Phylogeny As...

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45 – Summer 2009 Understanding Phylogeny As most of you realize, graphs are a useful way to present and summarize data. Scientists analyze large amounts of data to try and recreate the evolutionary history of various species. They use phylogentic trees to illustrate these relationships. A model phylogentic tree is shown in figure 1. A brief introduction will be presented on “how to read/interpret” these trees. After that a brief introduction will be presented on “how to construct” these trees. Our website will have various trees that depict the relationship of the various groups that you will examine in Bio 1AL. It is important to realize that scientists use various computer programs to construct these trees. Different scientists, using the exact same data can construct different trees by varying the weighting of different characteristics. Truth is, scientists even debate what a “characteristic” is. They are not infallible. The trees should illustrate a genealogy of “what begat what” as determined by scientists. Figure 1. Phlyogenetic tree illustrating pertinent features. A taxon (pl = taxa) refers to a named group of individuals that can vary from the species level (or even to the gene level) to larger groups, such as crustaceans or mollusks. The tree consists of branches, nodes (where the branch points occur), and tips. Tips can represent either an extant or extinct taxon.
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Bio1AL_Sum09_lab8_cladistics - Understanding Phylogeny As...

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