LECTURE 4 Flashcards
why is it important to read evolutionary trees?
they are not specific to evolutionary biology, it is very broad and included in many different disciplines
What is an evolutionary tree?
hypothesis about the history of descent with modification from a common ancestor that produces a suite of descendants
Transitions
evolutionary modifications appearing as species diverge
polytomy
relationships that cannot be fully resolved to dichotomies
soft polytomy
not enough information
hard polytomy
resulting from a split in the tree when we cannot distinguish who split from who first
Apomorphic (2 sister taxa)
evolutionary novelty = derived character
plesiomorphic
ancestral character
autamorphic
derived character unique to one group
synamorphic
derived character shared by two or more groups
homoplasic
character shared by a set of species but not present in their common ancestor
monophyletic group
(clade)
- group consisting of an ancestor and all its descendants
pholyphyletic group
group excluding an ancestor and including some, but not all, its descendants
paraphyletic group
group consisting of an ancestor and some, but not all of its descendants.
Steps of Parsimony analysis
- evaluate each character on each possible tree
- look for simplest evolutionary scenario explaining characters distribution among species at tips
- add up total number of evolutionary changes required by each scenario (hypotheses)
- identify which hypothesis requires fewest evolutionary changes
