Exam 3 Flashcards
Phylogenetic trees
Illustrate hypothesized evolutionary relationships
Best inference based on available data
Subject to change
Node
Point of divergence on phylogenetic tree
Speciation event
Extant species
Living species
What determines the relatedness of 2 species?
How recently they shared a common ancestor
NOT number of nodes separating them
NOT how close they are on the tree
Character state reconstruction
Inferring evolutionary history of traits based on their distribution in extant species
Follows principle of maximum parsimony
Maximum parsimony
Maximum likeliness
Simpler explanations are favored
Simpler= fewer evolutionary transitions
Evolutionary transition
Gain or loss of a trait
Constructing trees
Follows principle that close relatives share more traits than distant relatives
Assumes maximum parsimony
Choose set of traits to compare among species
Construct all possible trees
Count how many trait transitions must occur for each tree
The most likely tree has the fewest transitions
Choosing traits for character state reconcstruction
More is better
May be morphologic or genetic
Beware of “noise” in data set
Noise
Information that can lead you astray
2 sources of noise
Convergent evolution
Reversals
Convergent evolution
Leads to analogous traits
2 reasons traits may be similar
Homology or analogy
Homologous traits
Traits that are similar between species because they were inherited from a common ancestor
Often useful when constructing trees
Analogous traits
Traits that are similar between species because of same selection pressure, NOT inheritance from common ancestor
Lead to convergent evolution
Not helpful for trees
Look at gene expression and try knocking out genes to see if traits are analogous
Reversals
Derived traits revert to ancestral form
Ex: Body fur that we lost over time
Evidence of Evolution MUST demonstrate
Change over time
Common ancestry
7 Evidences of evolution
- Artificial Selection
- Fossils
- Vestigial structures
- Homology
- Genetic analysis
- Biogeography
- Natural Selection in Action
* All support each other as well
Artificial selection
Demonstrates that organisms can change; they’re not fixed in form
Genetic analysis
- The more closely related 2 species are according to the fossil record, the more similar their DNA’s, as would be predicted by common ancestry
- The universality of the genetic code
- Phylogenetic patterns in ERVs
Endemic species def.
Species found nowhere else
Natural selection in action
Evolution we can see happening quickly
Ex: evolution of body size in finches; evolution of drug resistance in bacteria/viruses
Sickle-cell alleles take home messages
Selection and drift act on allele frequencies simultaneously
Selection is subject to trade-offs, which vary across environments
Evolution is quantitative
