The evolutionary history of a species

The study/process of tracing the phylogeny of organisms to construct an evolutionary “Big Picture” relationships

Chapter 26: Phylogeny and the Tree of LifePhylogeny Systematics

Tools of Study: Taxonomy and Cladograms

A. Tool #1 Taxonomy Taxonomic categories are incorporated into cladograms

Phylogenetic Tree

Taxonomy Lingo:

1. Taxon: The taxonomic group at any levelTaxa (plural)

Note proper form:

1. Genus Capitalized;

species small case,

2.Both in italics or underlined

(Phylocode) Taxonomic systems totally based on evolutionary relationships

2. Branch Point / Node: The divergence of 2 taxa from a common ancestor3. Sister taxa: Taxa that share the most recent common ancestor4. Rooted:

5. Polytomy:

Branch Point (node)

Sister Taxa

Oldest branch to the leftA branch of more than 2 immediate descendents showing unclear evolutionary relationships

Mustela frenata

polytomy

Branch length can represent time or genetic change!

6. Monophyletic taxon

7. Paraphyletic taxon

8. Polyphyletic taxon

Contains all members of the same ancestry. This is the only valid taxon derived from a cladogram

Invalid taxon because it consists of a group of some with similar ancestry (I&K), but not all (J plus A and all its descendents) of the ancestors or descendants

Invalid taxon because it contains members that lack a common ancestor

Cladograms & Proper Taxonomic Categories (Taxon)

“one tribe”

Mammalia

Carnivora

CanideaFelidea

leopard cat Wolf Dog

Perisodactyla

Horse Zebra

Mammalia

Carnivora

CanideaFelidea

leapard cat Wolf

Perisodactyla

Horse Zebra

Mammalia

Carnivora

CanideaFelidea

leopard cat Wolf

Perisodactyla

Horse Zebra

Dog

Dog

Vertebral Column

Jaws

Four walking legs

Amniotic Egg

Hair

Outgroup

Shared primitive character

Shared derived characters

Clade

LampreyTuna

SalamanderTurtle

Leopard

A phylogenic tree with a series of 2 way branches that present the divergence of related organisms through a common ancestor

Tool #2 The Cladogram

Ingroup

Lancelet

7. Maximum Parsimony (Occam’s Razor)

Cladogram Lingo:

A branch in the cladogram

Traits (characters) that are of similar ancestry

The trait that is found in all members of the cladogram

The trait found in the continuing branch of the cladogram

The comparative organism that does not have the shared primitive character

The members of the cladogram that all have the shared primitive character

b) More complex structures evolve from simpler structures

1. Clade

2. Homologous Characters

3. Shared primitive character

4. Shared derived character

6. Ingroup

5. Outgroup

Protists - development of multicellularity

Exception: Parasites

The assumption that the simplest arrangement with the fewest required changes is the best explanation. Assumptions of parsimony include:

It is more likely that a unique feature evolves only once and passed down as opposed to evolving twice in different groups

a)

Exceptions: Birds - 4 chambered heart

#3 – Organism’s genome contains in evolutionary history

A. Different genes evolve at different rates

1. DNA coding for ribosomal RNA (rRNA) changes slowly, best used when taxa diverged 100s mya

2. Mitochondrial DNA (mtDNA) evolves rapidly, best used when exploring recent events

B. Gene duplicationUnequal crossing over during Prophase I that generates new genetic material, leading to molecular evolution

~Forms gene families: groups of related genes within an organism’s genome

1. Orthologous genes - homologous genes found in different species because of SPECIATION

2. Paralogous genes - formed from gene duplication, found in more than one copy in the SAME GENOME

Ex. Human α-globin and β-globin genes (proteins on surface of RBCs)

Gene Duplication due to unequal crossing over Slide 5

Model for Evolution of Human Globin Genes

Slide 18

Slide 5

Slide 5

Applying the Principle of Parsimony

Slide 2

Slide 2

Traditional Cladogram“The Mammal- Bird Clade”

New Cladogram“The Bird-Reptile Clade”

Parsimony and the Analogy-verse-Homology Pitfall

New evidence from other derived characters place birds with reptiles

Four chambered heart evolved twice thus it is an analogous character not a homologous character

Example of PolytomyNormal (dichotomous)

phylogenyPolytomy in phylogeny

-At all branch points there are two immediate descendants

-There’s a polytomy from which dragonflies, mayflies, & beetles arise, indicating that the relationships between these three lineages is not yet clear

Slide 2

Branch Length Representing Genetic Change

Branch Length Indicating Time

Slide 3