Phylogeny Tree

What does a phylogeny tree show?

Evolutionary relationships among organisms or taxa.

In a phylogeny tree, what does t=0 represent?

The starting point (bottom of the tree), representing the past.

What does the top of the phylogeny tree represent?

Present-day organisms (extant taxa).

What does each dot or branching point on a phylogeny tree represent?

A node, where a bifurcation (speciation event) occurred.

What does each node represent?

A common ancestor of the taxa branching from that node.

What does it mean when two taxa share a common ancestor?

They are sister taxa.

How are traits shown on a phylogeny tree?

As lines or markers on branches where the trait evolved.

What does it mean if traits are binary?

They are either present or absent.

What are multi-state traits?

Traits with multiple possible forms (e.g., endoskeleton, exoskeleton, hydrostatic skeleton).

Can traits be lost or revert to a previous state?

Yes, traits can be lost or reverted during evolution.

What is an autapomorphy?

A derived trait unique to one taxon.

Example of an autapomorphy?

T8 is an autapomorphy for Taxon H.

What is a synapomorphy?

A derived trait shared by multiple taxa within a clade, but not all taxa.

Example of a synapomorphy?

T6 is a synapomorphy for taxa C, D, and E.

What is a symplesiomorphy?

An ancestral trait shared by all descendants from a common ancestor.

Example of a symplesiomorphy?

T12 is a symplesiomorphy on the tree.

What does monophyletic mean?

A group including a common ancestor and all its descendants.

What does paraphyletic mean?

A group including a common ancestor and some but not all descendants.

What does polyphyletic mean?

A group that leaves out both some ancestors and some descendants, often formed by convergent evolution.

What is a character matrix?

A table listing traits (characters) and which taxa have them.

What is a coded matrix?

A numerical version of the character matrix, where traits are coded as numbers.

What is the rule of parsimony?

The simplest tree with the fewest evolutionary changes is most likely correct.

What is the “Family Screwidae” exercise?

Using screw images to fill out a character matrix, code traits, and determine the most parsimonious tree.

What is the “Plants” exercise?

Building a phylogeny tree for plant specimens, filling in a character matrix, coding traits, and finding the most parsimonious tree using correct phyla names.