phylogeny

Systematics

Study of evolutionary relationships among organisms

What does the joining of twigs & branches represent ?

The pattern of common ancestry

Phenotypic similarity in organisms can mean?

Very little about their evolutionary relationship

Convergent evolution

2 species independently evolve similar characters when adapting to similar environments rather than through inheritance from a common ancestor

Where do existing species be placed on phylogenetic trees?

On twigs

Derived characters are..

Shared with the most recent common ancestor of a group but not prior ancestors

• not found in species below the branch point on a cladogram

• Shared by a species

Character

Features we examine on species when looking at makeup of organisms

• Any aspect of the phenotype —> morphology, physiology, behavior & DNA

• polarized by determining whether it is ancestral or derived

Similarity between species may not accurately predict evolutionary relationships due to… (3 things)

1. The variable rate of evolution

2. Convergent evolution

3. Evolutionary reversal

Why does convergent evolution sometimes cause unrelated species to have similar adaptations?

Similar habitats may favor similar adaptations

Ancestral character

A similarity that arose prior to the most recent common ancestor of a group

• A character is ancestral if it is shared with the out group

What species is the most recent common ancestor of chimps and gorillas in the diagram?

2

Taxa

Species or higher level groups

• genera / families

• Used in cladistic analysis

Character state

One of two or more variations of a character

Output

A species that does not have the trait

• closely related to the group under the study, but it's not a member of the group

• Can be used to polarize characters

• Our group comparison is used to determine whether a character is ancestral or derived

Shared derived character

Inherited from the most recent common ancestor

• hair in mammals

• Cladistic analysis

Cladogram

Depicts a hypothesis of evolutionary relationships

When systematists polarized a character, they are determining whether..

The character is older and ancestral, or if it is newer and derived

Clade

Common ancestor and all of its descendants

• ancestral species & all of it's descendants

Homoplasy

Share drive character state that has not been inherited from a common ancestor exhibiting that character state

• Result from convergent evolution or from evolutionary reversal

• Causes organisms to seem closely related when they're not

Causes of homoplasy

Evolutionary reversal & convergent evolution

Cladogram

Nesting clades, characterized by shared derived characters

How do systematics determine if a character is ancestral or derived?

They compare the characters of a group understudy to those of an out group