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17 Cards in this Set

  • Front
  • Back
Phylogenetics is the science of ________.
recontructing evolutionary trees
What's the first method of tree reconstuction?
1) Phenetics (based on grouping populations according to their similarities)
What are the steps involved in phenetics?
1) list similarities
2) group by counts of similarities
3) remember homology vs. homoplasy
What's the 2nd method of tree reconstruction?
cladistics (taxa grouped based on shared derived characters)
What are the assuptions of cladistics?
1) all taxa related by descent from a common ancestor
2) THese relationships take the form of a tree
3) Lineages within the tree change through time
Phenetic methods are also called _______ methods, especially when data are molecular.
Distance.. phenetics:
1) is computationally simple
2) ignores the fact that similarity can result from convergent evolution (homology vs. homoplasy)
3) has been replaced by newer and better methods
What is true about cladogenesis and shared-derived character states (synapomorphies)?
when a lineage splits after the evolution of a derived character state, both daughter lineages will have the derived character.
Define Synapomorphy
a shared-derived character
shared: occurs in 2 or more taxa
derived: a trait that has changed since the earliest common ancestor of the group
What are cladistic phylogenies solely based on?
What are 2 alternate pathways to similarity that can confound (throw into disorder)the recognition of synapomorphies?
1) symplesiomorphy: a primitive character state shared by 2 or more taxa. or apomorphy: a derived state found in only one taxon

2) Homoplasy: similarity resulting from convergent or parallel evolution
What are 2 strategies for avoiding homoplasy?
1. Choose characters that change rarely
2. Use many, many characters and hope to swamp any homoplasy with lots of synapomorphies
What are the steps of the OUTGROUP COMPARISON principle (of the cladistic method)?
1. choose an OUTGROUP known (on the basis of other evidence) to be OUTSIDE the group of interest
2. Character states present in the outgroup are assumed to be ancestral
3. Characater states present only in the ingrouup are synapomorphies (or apomorphies if only seen in one taxon)
What kinds of outgroups are most useful?
closely related ones...but still the outgroup must be outside the group of interest.
The second Cladistic methods principle is ?
Parsimony principle--the simplest answer is the best. Applied to phylogenetics: the evolutionary tree that requires the least amount of change is the most likely.
Determining whether character states are ancestral or derived via OUTGROUP COMPARISON is called _______
polarizing your characters
What are the difficulties with the parsimony principle?
finding the shortest tree
What are solutions to this problem?
1) use a computer to compare many trees
2) use a search algorithm to focus on only a subset of trees