classification and phylogenies taxonomic categories and taxa inferring phylogenies –the similarity...
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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
Chapter 2 Opener How do we classify organisms?
Morphological similarity occassionally obscurs relationships
Figure 2.5 An example of phylogenetic analysis applied to three data sets (Part 1)
Sometimes, phylogenies derived from similarities are congruent witha 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 2.10 Evidence for phylogenetic relationships among primates, based on the ψη-globin pseudogene
mtDNA4,700 base sequenceGenes for 11 tRNAs6 proteinsHuman-chimpanzee relationship1023 more likely thanChimpanzee-gorilla relationship
Y DNABase sequence forTestis-specific protein Y
Autosomal DNABase sequence ofBeta-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 therate of evolution
Y = a + bX
b = 0.016b = 0.019
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