Download Phylogeny - Perry Local Schools

Chapter 26
Phylogeny and the
Tree of Life
Chapter focus
• Shifting from the process of
how evolution works to the
pattern evolution produces
over time.
Phylogeny
• Phylon = tribe,
geny = genesis or origin
• The evolutionary history of a
species or a group of related
species.
Systematics
• The study of biological
diversity and classification.
• Uses evidence from the fossil
record and other sources to
reconstruct phylogeny.
Systematics fuses:
1. Phylogeny- tracing of
evolutionary relationships.
2. Taxonomy- the identification
and classification of species.
Taxonomy
• Natural to humans.
• Modern system developed by
Linnaeus in the 18th century.
Scientific names
• Composed of Genus and
species.
• Written in Latin and shown in
italics or underlined.
• Governed by a set of rules and
procedures.
Linnaeus Taxonomy
1. Binomial Nomenclature –
two names for each organism.
Ex - Homo sapiens
2. Hierarchical System –
arranges life into groups.
Ex - Kingdom  Species
Goal of Systematics
• To have Taxonomy reflect the
evolutionary affinities or
phylogeny of the organisms.
Phylogenetic Tree
• Branching diagram showing
evolutionary relationships
between organisms.
Phylogenetic tree Example
Trees show:
• Ancestral lineage
• Branch points or nodes
• Length of branch point
suggests “time” and degree of
closeness.
Phylogenetic tree Example
Ancestral Lineage
Branch point
Question?
• How to group taxa so that the
phylogenetic relationships are
correct ?
Ideal Situation
• Monophyletic Grouping - a
single ancestor gave rise to all
species in the taxon.
Other Possibilities
• Polyphyletic - grouping where
members are derived from two
or more ancestral forms.
• Paraphyletic - grouping that
does not include all members
from an ancestral form.
Problem
• Not all “likeness” is inherited
from a common ancestor.
• Problem is of homology vs
analogy.
Homology and Analogy
• Homology – likeness attributed
to shared ancestry.
– Ex: forelimbs of vertebrates
• Analogy – likeness due to
evolution solution for the same
problem.
– Ex: wings of insects and birds
Convergent Evolution
• When unrelated species have
similar adaptations to a
common environment. A
specific example of Analogy.
• Ex: Sharks and dolphins
Only 1 is a “mole”
Only one is a “cactus”
Need
• Methods to group organisms
by similarities and
phylogenies.
• One possible method is
Molecular Systematics.
Molecular Systematics
• Compares similarities at the
molecular level.
• Ex: DNA, Proteins
DNA patterns
• If similar DNA – more closely
related, more recent common
ancestor.
• If different DNA – less closely
related, less recent common
ancestor.
Making a Phylogenetic Tree
• May use morphology, genetic
and other data.
• Typically “rooted” in a
common ancestor.
• Uses statistical analysis
looking for “best fit”.
Best Fit
• Maximum parsimony –
requires fewest DNA base
changes.
• Branch lengths – suggest the
closeness of the relationships
and the time of branch points.
Evolutionary History
• Is in the organism’s genome.
• Note – taxonomic
relationships can be changed
based on what the DNA tells
us.
Result
• Taxonomy will become
Genealogies, reflecting the
organism’s
"Descent with Modification“.
Kingdom
• Highest Taxonomic category
in the Linnaeus system.
• Old system - 2 Kingdoms
1. Plant
2. Animal
5 Kingdom System
• R.H. Whittaker - 1969
• System most widely used, but
is changing.
Main Characteristics
•
•
•
•
Cell Type
Structure
Nutrition Mode
Problems in Kingdom Monera
and Protista
Current Views
• Multiple Kingdoms – split life
into as many as 8 kingdoms.
• Domains – a system of
classification that is higher
than kingdom.
3 Domain System
• Based on molecular structure
for evolutionary
relationships.
• Prokaryotes are not all alike
and should be recognized as
two groups.
3 Domains
1. Bacteria – prokaryotic.
2. Archaea – prokaryotic, but
biochemically similar to
eukaryotic cells.
3. Eucarya – the traditional
eukaryotic cells.
Tree of Life
Summary
• What is Phylogeny?
• What is a phylogenetic
tree?
• How is molecular data used
in phylogeny?
• Know the Domains and the
Tree of Life.