the evolutionary history of a species the study/process of tracing the phylogeny of organisms to...
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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)
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