Lecture 15 - Phylogenetics Flashcards
What is phylogenetics?
The study of evolutionary relationships among groups of organisms.
What is a phylogenetic tree?
A hypothesis of the order in which evolutionary events are assumed to have occurred.
Give the two directions which phylogenetic trees can be shown.
- Top to bottom
- Left to right
When did monocotyledons separate from dicotyledons?
200mya
What is a node?
Where one branch splits into two
What is a root?
The common ancestor for all those in the tree.
Which part of a phylogenetic tree represents a speciation event?
A node
What is an outgrip?
A taxon outside of the group of interest.
How do you fin the root in a tree?
Look for an outgroup.
What is a cladogram?
A phylogenetic tree formed using cladistic methods, showing branching pattern only (shows which are related to which).
- Involves classification into clades based on shared derived characteristics.
What is a synapomorphy?
A trait shared among species because the common ancestor of those species also had that trait.
Which should you look at when forming a phylogenetic tree: homologous or analogous characteristics?
Homologous
What is a homoplastic character state?
A trait that is shared by two or more taxa because of convergence, parallelism or reversal.
What is the modified nostrils on top of the head in cetaceans and dinosaur group Macronaria and example of?
Homoplastic character state
What are plesiomorphic characters?
An ancestral trait, which presence of does not give any information about relationships between species in the tree.
What is apomorphy?
A derived or specialised character.
What is autapomorphy?
A derived character that is found in only one taxon.
Why are autapomorphies not useful in trees
Because they don’t say which organism it is most related to.
What does a clade consist of?
An ancestor organism and all of its descendants, a monophyletic group.
What are phylogenetic groups based on?
Clades
What kind of group is the group ‘reptiles’?
A paraphyletic group
What is a paraphyletic group?
A group that contains the common ancestor, but not all of the descendants.
What is the class mammalia based on?
The synapomorphy of teeth
Give an example of a polyphyletic group.
‘Warm-blooded’ organisms
What is a phylogram?
A phylogenetic tree that has branch lengths proportional to the amount of character change.
What is a chronogram?
A phylogenetic tree that explicitly represents evolutionary time through its branch lengths.
What is parsimony?
Says that:
When constructing a phylogenetic tree, the best hypothesis is the one that requires the fewest evolutionary steps. :-)
