Chapter 5 Flashcards
Phylogenetic trees are used to
- construct hypotheses about common ancestors
- construct hypotheses about how various species are related to each other
- test hypotheses about the relationships between various species
The disadvantage of using distance methods to construct trees include the fact that
Distance methods lack any sort of underlying evolutionary model;
The assumption is made that similarity is a reflection of homology
The older the clade, the
more likely its members will show sequence divergence
The basic conceptual approach to phylogenetic tree building involves
- the process of collecting information about character states
- the process of selecting taxa for inclusion in the tree
- the logic that species with many character states in common are more closely related than those without
The basic conceptual approach to p-tree building assumes (part two):
That species with many character states are more closely related than those without;
That common characters are homologies
Phylogenetic methods developed by evolutionary biologists to find the best tree possible for the taxa being studied include:
Parsimony methods; Distance methods; Maximum Likelihood methods; Bayesian Inference methods
The fundamental idea behind parsimony is
That the best phylogeny is the one that both explains the observed character data and posits the fewest evolutionary changes
Parsimony analysis offers the advantage of
conceptual simplicity
Parsimony has the disadvantage of
Being an inconsistent estimator; Long-branch attraction
Long branch attraction is
The inferring of too close a relationship between a rapidly evolving species or populations
The Fitch algorithm is
Determines how many evolutionary changes are required for a given tree and character; Does not find the best tree
Which of the following statements regarding rooted trees is/ are true?
- Any two rooted trees corresponding to the same unrooted tree will require the same number of character changes;
- The most common approach to rooting a tree is to use an outgroup
Which of the following statements regarding rooted trees is/are true?
- We can form a rooted tree from an unrooted tree simply by picking a branch around to which to root the tree.
- Knowing the root of a tree, along with info about species ranges, can tell us about the PHYLOGEOGRAPHY of a group of species
Arrange the steps of constructing a phylogenetic tree using the distance method in the correct order
- The distance between species is measured using a character state changes
- A distance matrix is created
- Trees are constructed by arranging segments or branches derived from pair-wise distance comparisons
- Phylogenetic inference software is used to choose the best tree
How many different unrooted tree arrangements are possible for a phylogenetic tree relating 4 species?
THREE
The advantage of using distance methods to construct trees include the fact that
Distance methods are conceptually STRAIGHFORWARD; & computationally among the FASTEST techniques
How many unrooted trees are possible for 5 species?
15
Arrange bootstrap resampling in correct order
- A tree is constructed for the estimated phylogeny, based on the original character mix
- Resampling is done from original character mix to create a collection of bootstrap replicate data sets
- The same tree-building methods used on the original character set are used to create a collection of bootstrap replicate phylogenies
- To assess the support for any feature of the original tree, the percentage of replicate trees that also display that feature are calculated
Bootstrap resampling
- can be used with any technique for phylogenetic inference
- does not yield statistical significance levels
Once we have used character data to infer a tree, how can we be certain this tree is correct?
We can test statistical confidence certain features of the tree are correct
Computer programs for reconstructing large phylogenies
only check a very small fraction of possible trees
Which of the following statements concerning trees is true?
- Each unrooted tree corresponds to numerous rooted trees
- An unrooted tree with k species has 2k-3 branches
- An unrooted tree with k species has 2k-3 times as many rooted trees as unrooted trees
How many UNrooted trees are possible for 22-species tree
more than there are stars in the universe
How many Unrooted trees for a 6-species and 7-species tree, respectively?
105 and 945
