Download I. Phylogeny : evolutionary history

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Ch 20
A.Taxonomy: science of naming & classifying organisms
1. Linnaeus – binomial nomenclature = naming
2. Classifying = grouping
a. groups called taxa (singular = taxon)
b. original taxa were based on anatomy
c. re-classification based on evolutionary
relatedness
• B. Phylogenetic Tree – diagram of evolutionary
history of groups of organisms
• 1. A hypothesis about evolutionary relationships
• 2. diagram branches = dichotomies
• a. common ancestor represented by branch point
• b. common ancestor is no longer extant
• c. outgroups =
do not share that
common ancestor
• 3. sister taxa = groups that share an immediate
common ancestor
• 4. basal taxon = most recent common ancestor of all
taxa on tree
• 5. > 2 branches = indicates unclear relationship
• Armadillos and humans are sister groups in this tree
• 6. Phylogenetic Trees DO NOT….
• a. indicate absolute time, only relative order
• b. tell how much change occurred between taxa
• c. show that a species evolved from a sister species
•
***the common ancestor is extinct ****
• C. Phylogenetic Trees based on homology
• NOT analogy (analogous structures)
• 1. similar appearance & function
• 2. not inherited from common ancestor
• 3. different internal structures
• 4. different DNA/proteins indicate distant relation
• 5. result from convergent evolution
•
a. similar structures evolve independently
•
b. due to similar environmental pressures
•
c. organisms not closely related
• D. Molecular Homologies
• 1. based on number of differences in
•
a. nucleotides
•
b. amino acids
• 2. more differences = lest closely related
• a. more time for mutations to accumulate
•
•
•
•
1. groups called clades
2. must include all ancestors of the common A
3. clades called monophyletic
4. if a taxon includes descendants from more than
one common ancestor = polyphyletic
• 5. if a taxon does not include ALL of the
descendants = paraphyletic
• 6. based only on shared ancestral characters
• a. inherited from common ancestor
• b. not shared derived traits = traits new to group
•
not found in ancestors
• 7. follows maximum parsimony
• a. fewest branches is best
• b. fewest branches between outgroup (oldest) and
modern species