Transcript Chapter 25: Phylogeny and Systematics

Chapter 25: Phylogeny and
Systematics
Phylogeny = the evolutionary history of
a species
Systematics = study of biological
diversity in an evolutionary context /
reconstructing phylogeny
I. Fossil Record and Geologic
Time
A. Fossils
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Usually in sedimentary rock and the hard
stuff remains
Sometimes minerals seep in and replace
tissue
Sometimes thin films
Sometimes casts
Trace Fossils
Sometimes they die and don’t decompose
B. Dating Fossils
1.
Relative Dating
- gives a general idea of time line
- use sediment layers
- Precambrian, Paleozoic, Mesozoic,
Cenozoic
- separated by mass extinction
Video
B. Fossil Dating
2. Absolute Dating
- defines periods in years
- radiometric dating – measures
radioactive isotopes
- half-life
- ex. Carbon 14, Uranium 238
- L amino acids vs D amino acids
3. Fossils leave an incomplete record
C. Continental Drift and
Phylogeny
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Drifting of
continents leads to
speciation
Forming (250 million
years ago) and
breaking up (180
million years ago) of
Pangaea
D. Mass Extinction
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Fossils show long periods of gradual action
and then huge species turnover
Permian Mass Extinction – between Paleozoic
and Mesozoic / 90% of marine life died
Cretaceous Mass Extinction – between
Mesozoic and Cenozoic / maybe a comet,
firestorm, and volcanoes
There is a creative side to destruction
II. Systematics: Connecting
Classification to Phylogeny
A. Hierarchical System of
Classification
1. Binomial Nomenclature
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Genus species
Examples: Homo sapien
Drosophila melaganster
Canis lupus
Borellia burgdorferia
2. Hierarchical Classification
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Domain, Kingdom,
Phylum, Class,
Order, Family,
Genus, Species
Taxon – taxonomic
unit
Phylogenic tree –
based on taxonomic
grouping
Phylogenic Tree
B. Phylogenic Systematics
- Classification based on evolutionary
history
- Use fossil records, assess
relationships, compare anatomy, DNA
1. Clades
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Clade – evolutionary branch in a cladogram
(phylogenic tree)
Cladogram – phylogenic diagram based on
cladistics
Based on 2 way branching points
Each point represents a divergence from a
common ancestor
Monophyletic – ancestral species and
descendants (same as clade)
Paraphyletic – ancestor and some, not all, of its
descendents
Polypyletic – lacks a common ancestor
Cladogram
(phylogenic tree)
2. Constructing a Cladogram
a. Homology vs. Analogy
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Homology – likeness attributed to
shared ancestry
Analogy – similarities due to convergent
evolution
More homology = closer relationship
b. Identify Shared Derived
Characters (Traits)
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Shared Primitive Characters – homology
common to a group more inclusive then
others / ancestral / backbone in
mammals
Shared Derived Characters – unique to
a clade / hair in mammals
c. Perform Outgroup
Comparison
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Way to differentiate from derived and
primitive characters
Outgroup – species closely related to the
species being studied but less closely related
to any of the study group members (ingroup)
Ingroup – organisms being studied
Based on idea that homologies present in
ingroups and outgroups are primitive and
were present in a common ancestor
Cladistic Taxonomy
3. Phylogeny from Molecular
Data
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Compare genes by comparing DNA
sequences (proteins) and align the
sequences for comparison
4. Parsimony
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Nature should be the simplest explanation
consistent with the facts
5. Phylogenic Trees are
Hypotheses
6. Molecular Clocks
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Some parts of the genome evolve at a
constant rate
Graph the percent different in sequences
vs. time / AIDS