BSC2010 Unit 3 Lecture 7

Phylogeny

Evolutionary history of a group

2 ways to classify taxa

• Phylogenetics

• Taxonomy

Taxonomy

Hierarchical way of categorizing species started by Carolus Linnaeus

Binomial nomenclature

Two parts - genus and species name

Principle of parsimony

Simplest path uses the fewest evolutionary changes

Branch points represent ___.

speciation events

Sister taxa

Two taxa that are each other’s closest relatives (the two branches off a single node)

Sister species

Two species that are each other’s closest relatives

Sister clades

Any two clades that are each other’s closest relatives

Why can phylogenies rotate?

Only the branching relationships matter; the information if the same.

A clade is ___.

Monophyletic

Monophyletic

Includes the most recent common ancestor and all its descendents

How to recognize a monophyletic group/clade?

Can be cut from the tree with one snip

Paraphyletic

Group does not include all descendents of common ancestor

Polyphyletic

Group does not include common ancestor

How are evolutionary relationships reconstructed?

Shared characters → parsimony

Homologous trait

A similarity between two or more features that is due to inheritance from a common ancestor

Analogous trait

Biological features in different species that serve similar functions but evolved independently, not from a common ancestor

Synapomorphies

Shared, derived traits → evidence for common ancestry

Outgroup

Reference group that is closely related to group but lacks synapomorphies that unite the ingroup

Convergent evolution

Independent changes to the same trait in two or more groups of organisms

Example of analogous trait

Bat vs. bird wings

Evolutionary reversal

A character reverts from a derived state back ot an ancestral state

Homoplasies

Traits that are not inherited from a common ancestor; can be from convergent evolution and evolutionary reversal