Biology 1001A Lecture Notes - Lecture 20: Synapomorphy, Divergent Evolution, Ingroups And Outgroups
3 Apr 2016
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Document Summary
Phylogenies very often involve reconstructing evolutionary relationships and need to know about the types of traits that the most recent common ancestor of a group of species had. Outgroup comparison relies on parsimony: simplest explanation is best. Whichever tree requires the fewest evolutionary changes (gains or losses of a trait), is probably correct. More likely than being evolved separately (multiple appearances) Outgroup shouldn"t be too closely related to one species and shouldn"t be too distant. Outgroup: shark: no milk, no fur, no wings, no beak. Ingroup: chicken: no milk, no fur, wings, beak, bat: milk, fur, wings, no beak, chipmunk: milk, fur, no wings, no beak. Not all similarities are equally informative (only synapomorphies: synapomorphies are shared and derived. No: not shared the beak is autopomorphy. Tree on the left is most parsimonious better supported. Minimum number of evolutionary steps: left tree: 4, right: 5.
