26.3 Shared Characters are Used to Construct Phylogenetic Trees

Question 1

What is Cladistics?

Answer 1

An approach to biological classification in which organisms are categorized based on shared derived characteristics that can be traced to a group’s MOST RECENT common ancestor and are not present in more distant ancestors.

Question 2

What are Clades?

Answer 2

A group of species, each of which includes an ancestral species and all of it’s descendants (monophyletic).

Question 3

What is the difference between Monophyletic, Paraphyletic, and Polyphyletic?

Answer 3

Monophyletic: group consisting of an ancestral species and all of it’s descendants.

Paraphyletic: group consisting of an ancestral species and some, but not all, of it’s descendants.

Polyphyletic: group which includes taxa with different ancestors.

Question 4

What is a Shared Ancestral Character?

Answer 4

A character that originated in an ancestor of the taxon.

Question 5

What is an Outgroup?

Answer 5

A species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes the species we are studying (the Ingroup).

Question 6

What is a Shared Derived Character?

Answer 6

An evolutionary novelty unique to a clade.

Question 7

What is a Cladogram?

Answer 7

A cladogram is a branching diagram (tree) assumed to be an estimate of a phylogeny where the branches are of equal length. Therefore, cladograms show common ancestry, but do not indicate the amount of evolutionary “time” separating taxa.

Question 8

What is a Phylogram?

Answer 8

A phylogram is a branching diagram (tree) that is assumed to be an estimate of a phylogeny. The branch lengths are proportional to the amount of inferred evolutionary change.

Question 9

What does branch length depend on when making a phylogenic tree?

Answer 9

It depends on the rate of change for different genes, as different genes evolve at different rates, which affects the branches length.