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. Symplesiomorphies cannot show common ancestry within the group because they evolved earlier in the hierarchy.

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

Combining trees

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

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

Molecular Systematics

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

ITS - Internal Transcribed Spacer region of ribosomal DNA

Molecular characters Point mutations Insertions Deletions Inversions

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

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

Angiosperm Phylogeny Group Angiosperms

Angiosperm Phylogeny Group Eudicots