Transcript Chapter 25 -- Systematics and the Phylogenetic Revolution

Chapter 25 -- Systematics and
the Phylogenetic Revolution
How to connect the dots of
organisms?
What are the traditions of classification?
 1st classification was into plants or animals
 Traditional language used
 Grouped into general groups
 Descriptive terms followed
 Linneaus developed binomial nomenclature
 Rules?
Dichotomous Keys
 Organism is classified, key helps identify in
the field
 Presence or absence of trait
Taxonomy (arranging rules) is one of the
current sciences of classifying organisms
 1.No two organisms have the same name.
 2. All names are in Latin.
 3.The first word is capitalized and refers to
the genus.
 4.The second word is lowercase and refers
to the species.
 5.The two words combined are the scientific
name and are written in italics.
 6.The first word can be abbreviated after the
first use in text.
 Taxonomy is organized in a hierarchy.
 Taxon is one level. These organisms share
decided traits.
Genus
Family
Order
Class
Phylum
Kingdom
What if new information does not fit the
classification models from years ago?
 Incomplete fossil record
errors are being
corrected by
biochemical analysis.
 Systematics reconstruction and
study evolutionary
relationships.
 *determine common
ancestor and create tree
based on order of evolution
There are some problems in this
process that require critical thinking
while examining the trees.
* Evolution does not occur at a constant rate
* Evolution is not unidirectional
* Location will influence the amount of
selective pressure an organism experiences.
* Convergent evolution may independently
evolve and appear to be similar.
Similarities are polarized (classified) as
ancestral or derived.
 * Ancestral characteristics are called
pleisomorphic.
 * The group that inherited is called
sympleisomorphic. (Example – four legs are a
shared characteristic by many mammals)
 * Derived (apomorphic) characteristics are
characteristics that occur during speciation or a
split. These characteristics are often states –
they are present or they aren’t present.
It is difficult to tell if a similarity is ancestral or
derived.
a. An organism that is
closely related, but not a
member of the group you
are comparing is chosen
as an outgroup.
b. Characteristics displayed
by the outgroup are
assumed to be ancestral
The presence or absence of a similarity can
then be recorded and used to a cladogram.
• Clades are nested inside of each other and the
derived trait shared by the members are called
synamorphies.
• A cladogram does not include all species and does
not show the common ancestor at the node where
two branched off.

Be aware of convergent evolution
 The principle of parsimony favors any hypothesis of fewest
assumptions.
 The principle of parsimony does not always apply when
evolution occurs quickly – such as in DNA exons.
 Molecular clocks use a reliable gene to track mutations that have
occurred to determine how frequently a mutuation occurs.
 (.5 changes/base pair/billion years; 4 b.p. changes = ___ years)
Graphical explanation of basic Phylogenetic terms
Monophyletic taxon : A group composed
of a collection of organisms, including the
most recent common ancestor of all those
organisms and all the descendants of that
most recent common ancestor. A
monophyletic taxon is also called a clade.
Examples : Mammalia, Aves (birds),
angiosperms, insects, etc.
Paraphyletic taxon : A group
composed of a collection of
organisms, including the most recent
common ancestor of all those
organisms. Unlike a monophyletic
group, a paraphyletic taxon does not
include all the descendants of the
most recent common ancestor.
Examples : Traditionally defined
Dinosauria, fish, gymnosperms,
invertebrates, protists, etc.
Polyphyletic taxon : A group composed
of a collection of organisms in which
the most recent common ancestor of all
the included organisms is not included,
usually because the common ancestor
lacks the characteristics of the group.
Polyphyletic taxa are considered
"unnatural", and usually are reclassified
once they are discovered to be
polyphyletic.
Examples : marine mammals, bipedal
mammals, flying vertebrates, trees,
algae, etc.
Comparative Anatomy
* Homologous or Analogous?
* Variation is not because of single mutations
How is life currently grouped?

Changes in
classification

Plants,
animals…

Carl Woese
The domain Bacteria has the
largest amount of organisms.

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a. Bacteria have important
roles in the biosphere
including nitrogen fixation
and photosynthesis.
b. Bacteria also cause
many diseases.
c. Taxonomists recognize
12-15 groups of bacteria.
Archaea (ancient) appear to be more closely
related to eukaryotes
a.
It is a diverse group, but has distinct
characteristics that separate these prokaryotes
from other organisms.
 They have cell walls – but no
peptidoglycan.
 The lipids in the cell membrane are
unique from all other organisms.
 Their ribosomal RNA sequences are
distinct.
 Some archaea genes have introns.
There are three general categories of Archaea
based on their environments or metabolic
pathways.
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Methanogens are strict anaerobes
 * use H2 gas to convert CO2 to CH4. They live
in swamps, marshes, and the intestines of
mammals.
Extremophiles
 thermophiles = 121 C, halophiles = 15-20%
salinity = Dead Sea, extreme pH (.7 – 11) and
extreme pressure (must have 300 atm to
survive, need 800 atm).
Nonextreme archaebacteria grow in the same
environments as bacteria, but have signature DNA
sequences. (genome = only 500 base pairs long)
The domain Eukarya
appeared 1 billion years
after prokaryotes.
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Protista
Led to plants, fungi and animals
Endosymbiont Theory
• Compartmentalization
• Multicellularity
• Sexuality
Viruses don’t fit into a
kingdom
 Not cellular
 Infectious
 TMV