Classification and Phylogenies Taxonomic categories and taxa Inferring phylogenies –The similarity vs. shared derived character states –Homoplasy –Maximum parsimony, maximum likelihood, and Baysian methods –An example of phylogenetic analysis –Molecular clocks and timing of branching events –Difficulties in Phylogenetic Analysis
Taxonomic categories –Species –Genus –Family –Order –Class –Phylum –Division
Chapter 2 Opener How do we classify organisms? Morphological similarity occassionally obscurs relationships
Figure 2.2 Darwin’s representation of hypothetical phylogenetic relationships
Figure 2.1 The Tree of Life
Figure 2.5 An example of phylogenetic analysis applied to three data sets (Part 1) Sometimes, phylogenies derived from similarities are congruent with a phylogeny derived from synapomorphies
Figure 2.5 An example of phylogenetic analysis applied to three data sets (Part 2) Similarities can produce an incorrect phylogeny
Figure 2.5 An example of phylogenetic analysis applied to three data sets (Part 3) Homoplasies confound phylogeny reconstruction
Figure 2.6 Monophyletic groups whose members share derived character states that evolved only once Easy reconstruction
Figure 2.7 Two possible hypotheses for the phylogenetic relationships of humans Principle of parsimony: Okkam’s razor
Figure 2.9 Members of the primate superfamily Hominoidea Phenetic vs. cladistic classifications
Figure 2.10 Evidence for phylogenetic relationships among primates, based on the ψη-globin pseudogene
mtDNA 4,700 base sequence Genes for 11 tRNAs 6 proteins Human-chimpanzee relationship more likely than Chimpanzee-gorilla relationship Y DNA Base sequence for Testis-specific protein Y Autosomal DNA Base sequence of Beta-globin gen cluster
Figure 2.11 Relationships among major groups of vertebrates Morphological and DNA sequences sometimes reveal the same phylogeny
Figure 2.13 (A) If divergence occurred at a nearly constant rate, relative times of divergence of lineages could be determined from differences/similarities between taxa and phylogeny of the taxa could then be estimated. (B) Hypothetical phylogeny in which evolution occurs at a nearly constant rate
Figure 2.14 Calibration of molecular clocks in Hawaiian organisms Slope of regression reveals the rate of evolution Y = a + bX b = b = 0.019
Fruit fly divergence: Hawaiian Islands Results of speciation
Figure 2.15 The relative rate test for constancy of the rate of molecular divergence
Difficulties in phylogenetic reconstruction 1. Scoring characters 2. Homoplasy 3. Past evolutionary events may be obscured by recent evolution. 4. Polytomy 5. Gene trees and character trees can be incongruent 6. ± hybridization and horizontal allele transfer
Figure 2.23 Hybridization and reticulate evolution
Figure 2.24 Phylogenies of some Old World monkeys and cats