Biology Lecture No. 17: Phylogeny
Wednesday, November 9 , 2011
What Is Phylogeny? :
-Pattern of evolutionary relationships among organisms.
-Phylogeny reconstructs this relationship common among all organisms.
-Living modern species or groups at tips; common ancestors at the nodes.
-The rotation or reflection of any node(s) has no effect on the evolutionary timeline of organisms
displayed in the phylogeny.
Principles Of Phylogenetics:
-Evolutionary relationships among organisms reflect how recently (in time) groups of organisms shared a
-Phylogenies are constructed using patterns of similarity (the more similar things are the more recently
they shared a common ancestor)
-Homology: When similarity usually reflects recently shared ancestry.
Homology Vs. Homoplasy:
-Not all similarity reflects recent common ancestry. Not all similarities are synapomorphies.
-Convergence: Misleading similarity despite distant evolutionary relationship. E.g. bug wings, bird wings;
whale sonar, bat sonar.
-Divergence: Misleading dissimilarity despite close evolutionary relationship. E.g. Darwin’s finches.
-Traits that are homologous support true phylogeny, but homoplasious traits will mislead one
-What if one cannot distinguish a trait that is hom