9/16 Lecture + Pre-Class Videos

Pre-Class Videos: Interpreting Phylogenetic Trees, Phylogenetic Ancestors and Groups, Distinguishing Synapomorphies

What are Phylogenies and what is one way they are represented?

show the evolutionary history of relationships between organisms and their genes, often shown in a phylogenetic tree

Phylogenetic Trees (what is it and describe it)

models that represent currently supported evolutionary relationships

They have:

• a time axis that runs from root to tips

• a root

• at least two tips

• nodes

• lineage lines

The Phylogenetic Tree of Life shows…

the complete evolutionary history of life

What are Lineages and why are they created? How are they shown in a phylogenetic tree?

What is the result of a lineage diverging?

a series of ancestral and descendant populations draw as a line on a time axis

can split into independent lineages (usually two) that evolve traits independently

• New traits can be shown as dots on the lineage line and are assumed to be present in all descendant populations (though traits can be lost in some cases)

the distance between neighboring lineage lines doesn’t mean anything

Nodes (what they represent, how they are positioned)

where ancestral populations diverge into independent lineages

Positioned based on relative times of divergence

What is the MRCA? How does it connect to relatedness?

the most recent common ancestor

A more recent common ancestor between two groups usually means that those two groups are more closely related.

What are Taxonomic Groups (Taxa, Taxon)?

They can be…

Three classifications for taxa are…

groups of organisms that are compared in phylogenetic trees

can be species or groups of species (e.g. mammals)

can be classified as monophyletic, paraphyletic, or polyphyletic

What is included in a Clade (Monophyletic Group)?

includes an MRCA and all of that MRCA’s descendants

those descendants can be multiple species or just one species

What is included in a Paraphyletic Group?

includes a MRCA and some descendants (not all)

What is included in a Polyphyletic Group?

includes descendants from multiple different ancestors but doesn’t include the MRCA

What are Homologous Traits and how are they derived?

traits shared among different Taxa, derived from a common ancestor

What is a Synapomorphy?

a clade-specific homologous trait that is derived from that clade’s most recent common ancestor

This trait doesn’t appear in groups outside of the clade (otherwise it is only a homologous trait, not a synapomorphy).

Compare Extant vs Extinct

Extant: still existing

Extinct: no longer exists