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Cladistics and Molecular Systematics

Cladistics and Molecular Systematics. Depicting evolutionary changes. Homology. Homoplasy. Grouping rules. Only synapomorphies are evidence for common ancestry relationships. Convergences and parallelisms evolved independently so they cannot provide information about common ancestry.

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Cladistics and Molecular Systematics

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  1. Cladistics and Molecular Systematics

  2. Depicting evolutionary changes

  3. Homology

  4. Homoplasy

  5. 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.

  6. Parsimony • Most common method of choosing among trees • Minimizes evolutionary change • Occam’s Razor - Do not generate a hypothesis any more complex than the data demands

  7. Combining trees

  8. Characters for Cladistics • Qualitative – presence / absence • Multistate • Meristic – counting parts • Quantitative – measurements

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

  10. Molecular Systematics

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

  12. ITS - Internal Transcribed Spacer region of ribosomal DNA

  13. Molecular characters • Point mutations • Insertions • Deletions • Inversions

  14. 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

  15. 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

  16. Angiosperm Phylogeny Group • Angiosperms

  17. Angiosperm Phylogeny Group • Eudicots

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