BIOL 121 Lecture Notes - Lecture 22: Cladistics, Ichthyosaur, Genetic Distance
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BIOL 121 Full Course Notes
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Document Summary
Species divergence is the outcome of selection and evolution. How do biologists study the history of life on earth? (2: construct phylogenies, fossil record. Is the evolutionary history of a group of organisms. Phylogenies are usually summarized and depicted in the form of a phylogenetic tree. Shows the ancestor-descendant relationships among populations or species, and clarifies who is related to whom. In a phylogenetic tree, a branch represents a population through time; the point where two branches diverge is a node that represents the time when an ancestral group split into 2+ descent groups. The endpoint of a branch represents a group (a species or larger taxon) living today, or one that went extinct (dead end) Phylogenetic trees are an extremely effective way of summarizing data on the evolutionary history of a group of organisms. However, the genealogical relationships among species cannot be known with absolute certainty but are instead estimated from given data.
