BIOLOGY 1M03 Lecture Notes - Phylogenetic Tree, Cambrian Explosion, Hox Gene
24 Nov 2013
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Document Summary
Chapter 27: phylogenies and the history of life. The evolutionary history of a group of organisms is called its phylogeny. Phylogenies are usually summarized and depicted in the form of a phylogenetic tree. 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, called a node, represents the point in time when an ancestral group split into two or more descendant groups. A tip, the endpoint of a branch, represents a group living today or one that ended in extinction. Phenetic approach to estimating trees is based on computing a statistic that summarizes the overall similarity among populations, based on data. Researchers might use gene sequences to compute an overall. A genetic distance summarizes the average percentage of bases in a dna sequence that differ between two populations.
