Cladistics and Molecular Systematics

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Cladistics and Molecular Systematics
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Depicting evolutionary changes
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Homology
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Homoplasy
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Grouping rules

• Only synapomorphies are evidence for common
  ancestry relationships.
• Convergences and parallelisms evolved
  independently so they cannot provide information
  about common ancestry.
• Symplesiomorphies cannot show common ancestry
  within the group because they evolved earlier in
  the hierarchy.

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Parsimony

• Most common method of choosing among trees
• Minimizes evolutionary change
• Occams Razor - Do not generate a hypothesis any
  more complex than the data demands

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Combining trees
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Characters for Cladistics

• Qualitative presence / absence
• Multistate
• Meristic counting parts
• Quantitative measurements

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Morphological characters

• Limited numbers of characters
• Many characters vary continuously
• Homologies may be hard to discern

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Molecular Systematics
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Plant Genomes

• Chloroplast 135-160 kbp (cpDNA)
• Mitochondrion 200-2,500 kbp (mtDNA)
• Nucleus 1.1 x 106 - 110 x 109

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ITS - Internal Transcribed Spacer region of
ribosomal DNA
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Molecular characters

• Point mutations
• Insertions
• Deletions
• Inversions

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Molecular characters

• Enormous numbers of characters
• Four states for each character
• Different parts of the genome accumulate
  mutations at different rates possible to
  examine relationships at different levels

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Classifications

• Artificial group taxa according to similarities
  
• Natural group taxa according to evolutionary
  relationships
• Traditional intuitive
• Phenetic based on similarities
• Cladistic based on evolutionary links

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• Angiosperm Phylogeny Group
• Angiosperms

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• Angiosperm Phylogeny Group
• Eudicots