Week 2: Phylogeny and Evolutionary History Flashcards
What is Linnaean taxonomy?
arranged organisms in hierarchical classification.
What is phylogenetic systematics?
classify organisms according to evolutionary history.
What is phylogeny?
branching relationships of populations as they give rise to multiple descendant populations over evolutionary time.
What are characters?
any observable characteristics of organisms.
What are traits? Why are they critical to phylogeny?
specific values of a character (ie. brown fur). Traits are critical to phylogeny because 1) use observations of traits to infer patterns of ancestry - represent as a phylogenetic tree. 2) By mapping additional traits onto phylogeny already created, we can study sequence and timing of evolutionary events.
What is parsimony?
the relationships that requires the smallest number of character changes is most likely to be correct.
What is an outgroup?
is a taxon related to the groups of interest but branched off earlier in history.
What is a sister taxa?
derived from same node
What is a polytomy?
a node with more than two branches - relationships between are uncertain.
What is a monophyletic group?
taxonomic group consisting of all descendants of most common ancestor and no other members.
What is a clade?
represents a group of species that share a single recent common ancestor.
What is a polyphyletic group?
is not a monophyletic group - do not represent proper evolutionary clades - most are no longer used in modern systematics.
What is a paraphyletic group?
contains groups most common ancestor but not all its descendants.
What are rooted vs. unrooted trees?
Rooted trees - common lineage. Unrooted trees - do not indicate direction of time - branch tips represent more recent species than those represented by interior nodes - correspond to rooted trees. If unrooted tree has k branches - there are k corresponding rooted trees.
What are the differences between cladograms, phylograms and chronograms?
Trees without different branch lengths are cladograms and trees with are phylograms. Trees in which branch lengths represent actual time are chronograms.
What is a homologous trait?
found on 2+ species because they have inherited them from ancestor.
What is an analogous trait?
shared by 2+ species - not because of common descent - because of some other evolutionary process (usually natural selection) has independently fashioned similar traits in each species
What is divergent evolution?
closely related populations diverge because natural selection operates differently on each of them.
What is convergent evolution? And an example?
2 or more populations become more similar because they are exposed to similar selective conditions. aposematic coloration in frogs - bright warning colors. Aposematic coloration and toxicity are polyphyletic - caused by convergent evolution
What is a derived trait?
derived from ancestor
What is a synapomorphy?
shared derived trait - help uncover evolutionary relationships.
What is a homoplasy?
An analogous trait is homoplasy - trait similar in 2+ species but was not present in a common ancestor - can be misleading when constructing evolutionary tree.
What is a symplesiomorphy?
Symplesiomorphy - very recently derived and is not shared
How should you avoid being confused when making phylogenetic trees?
To avoid being confused 1. pick traits likely to be synapomorphies rather than symplesiomorphies. 2. Use a large number of characters. 3. Use an outgroup - one with known evolutionary relationship to the taxon we are studying - by using multiple - better estimate the polarity - order of appearance of traits using.
How do we combat misleading phylogenies derived from morphological characteristics>
Phylogenies derived from morphological characteristics can be misleading - especially when multiple characters have undergone convergent evolution. Now, use DNA sequencing to combat this.
What is beneficial about adding traits to preexisting phylogenetic tree?
When traits are placed on a preexisting phylogenetic tree - hypotheses about when traits evolved and which traits may be shared among which groups of relatives.
What are vestigial traits and 3 explanations for them?
Vestigial traits - have no known current function but appear to have been important in past. 3 explanations: 1) trait is not costly to organism - natural selection does not act against it. 2) There is some natural selection against it or it would have been lost. 3) the trait has some function that we have not identified - making it not vestigial. Can help us find evolutionary relationships.
