7.9 Phylogeny

Systematics

classification of organisms and determining their evolutionary relationships

Taxonomy

naming and classifying species

Phylogenetics

hypothesis of evolutionary history

use phylogenetic trees to show evolution

Determining Evolutionary Relationships

to determine evolutionary relationships, scientists use:

fossil records

DNA

proteins

homologous structures

Phylogenetic Trees

diagrams that represent the evolutionary history of a group organisms

similar to cladograms, except trees show the amount of change over time measured by fossils

Cladograms

each line represents a lineage

each branching point is a node

nodes represent common ancestors

nodes and all branches from it are called clades

species in a clade have shared derived features

the root is the common ancestor of all species

2 clades that emerge from the same node are sister taxa

a lineage that evolved from the root and remains unbranched is the basal taxon

Synapomorphy

a derived character shared by clade members

Derived Characteristics

similarity inheried from the most recent common ancestor of an entire group

Ancestral Characteristic

similarity that arose prior to the common ancestor

Outgroup

a lineage that is the least closely related to the rest of the organisms

many cladograms and trees include an outgroup

Monophyletic Group

includes the most recent common ancestor of the group and all of its descendants (clade)

Paraphyletic Group

includes the most recent common ancestor of the group, but not all its descendants

Polyphyletic Group

Does not include the most recent common ancestor of all members of the group

Parsimony

if there are conflicts among characters, use the principle of parsimony

use the hypothesis that requires the fewest assumptions (DNA changes)