Phylogenies Flashcards
Phylogeny
the evolutionary history of a group of organisms
Phylogenic tree
graphical summary of this history, showing the evolutionary relationships among genes, populations, species, or higher taxa
Tree of life
the most universal of all phylogenetic trees, depicting the evolutionary relationships among all living organisms on Earth
nodes
forks in the tree
represent hypothetical common ancestors
Where are taxa located?
At the tips of the tree, never in the middle, even if some of the taxa are extinct
Sister groups
share a recent common ancestor at the node where their branches meet
What happens once species diverge?
Both species continue to evolve
Outgroup
a taxon that diverged prior to the taxa that are the focus of the study
a sister group
helps to root the tree
Polytomy
a node that depicts an ancestral branch dividing into 3 of more (rather than two) descendant branches
usually indicates where there was insufficient evidence to determine which taxa are more closely related
Are the number of nodes important?
No
Are phylogenetic trees exact?
No. They must be estimated through using a variety of data.
Phylogenetic trees are like hypotheses that can be tested and are often revised as new data becomes available
What is the first step in inferring evolutionary relationships?
Decide which taxa to compare
Decide which characteristics to use to compare
character or trait
any genetic, morphological, physiological, developmental, or behavioral characteristic to be studied
Willi Henning
developed the cladistic approach
Cladisitic approach
a way to estimate a phylogenetic tree
based on the principle that relationships among species can be reconstructed by identifying shared derived traits, called synapomorphies
synamorphy
a trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors
can include gaining and loosing characteristics
monophyletic group
an evolutionary unit that includes an ancestral population and all of its descendants, but no others
paraphyletic group
a group that includes an ancestral population and some of its descendants, but not all
can be if a trait was lost in one of the descendants, not all have it
parsimony
the most likely explanation or pattern is the one that assumes the fewest steps to reach a particular result
In cladistics are the length of the branches important?
No
How is parsimony implemented?
through computer programs
homoplasy
occurs when traits are similar for reasons OTHER than common ancestry
convergent evolution
the independent evolution of similar traits in distantly related organisms due to adaptation to similar environment and lifestyles
not due to common ancestry
What is a cause of homoplasy?
Convergent evolution
The whale example
Does not follow parsimony because the whale had to gain the pulley shaped astragalus and then loose it, but it is supported by fossils and DNA data
An example of a homoplasy
Cell walls in plants and fungi
They are made out of different materials
the best classification system…
most closely reflects evolutionary history
molecular systematics
the use of molecular genetics to study the evolution of relationships among individuals and species
Four chambered hearts of birds and mammals example
Their common ancestor only had a 3 chambered heart, so the four chambered heart in birds and mammals had to have evolved independently after they split from the common ancestor
Note: figure out how to do the last problem with most parismonous tree
do practice taking data and constructing the most parismonious tree
