Phylogenetic Systematics Flashcards
Systematics
study of the kinds of organisms and of the evolutionary relationships
-goal: to classify organisms naturally, so the various groups are meaningful
Taxonomy
Science of classification
Kingdom > phylum > class > order > Family > genus > species
Cladistics
method of inferring genealogy and classifying organisms exclusively on the basis of shared, derived, traits > Synapomorphy
Homology
similarity of a feature in different organisms due to shared ancestry
Homoplasy
similarity of a feature not due to a shared ancestry
Character
observable feature of an organism
Character polarity
order in which evo changes occurred
Synapomorphy
shared derived character
Plesiomorphy
shared ancestral character
Autapomorphy
derived character possessed by only one taxon on a tree
Character States
- Binary Character: Only two character states (Present or absent)
- Multistate Character: three or more states
- Missing data: character unobservable or unknown
Principle of Parsimony
-Simplest hypothesis is preferred
Tree Length
Minimum # of characters state transitions
Outgroup Comparison
taxon that are related to your study taxa, but do not fall within that group
Stratigraphic criterion
root placed on the taxon that appears earliest in the fossil record
Polytomy
representation of multiple equally probable relationships
Strict Consensus Tree
a way of summarizing multiple MPTs
Clad
an ancestor and all of its descendants
paraphyletic group
doesn’t contain all descendants of a given ancestor
Polyphyletic group
contains descendants from more than one immediate ancestor
Phylogenetic Systematics
devoloped by Willi Hennig
Search algorithms: Branch and Bound
- counts tree length as it is building tree
- finds exact solution, but doesn’t bother finishing construction of all trees
- only works for up to 25 taxa
Search Algorithms: Heuristic Search
- builds tree counts steps
- rearranges tree until shortest one found
- not guaranteed to find all MPTs
Consistency index
measure of homoplasy in characters
