Download Unit 6A

Lecture #1
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Chapter 22~
Descent with
Modification:
A Darwinian View
of Life
Evolution
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Evolution:
the change over time of the
genetic composition of
populations
Natural selection:
populations of organisms can
change over the generations if
individuals having certain heritable
traits leave more offspring than
others (differential reproductive
success)
Evolutionary adaptations:
a prevalence of inherited
characteristics that enhance
organisms’ survival and
reproduction
November 24, 1859
Evolutionary history
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Carolus Linnaeus (17071778)
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Gradualism: Geological
changes occur slowly over a
long period of time
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Populations: Economic
paper on the population
growth in England
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Evolution: Organisms adapt to
their environment and these
changes are inherited by
offspring
Gregor Mendel (1822-1884)
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Uniformitarianism: Geological
processes have not changed
throughout history
Charles Darwin (1809-1882)
Evolution: Organisms have
specific adaptations
Thomas Malthus (17661834)
Paleontology: The study of
fossils
Charles Lyell (1797-1875)
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Jean Baptist Lamarck (17441829)
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James Hutton (1726-1797)
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Taxonomy: the naming and
classification of organisms
Georges Cuvier (1769-1832)
Inheritance: Genetic inheritance
through pea plants
Alfred Wallace (1823-1913)
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Evolution: Natural Selection is
Evolution Time Line
Descent with Modification
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5 observations:
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1- Exponential fertility
2- Stable population
size
3- Limited resources
4- Individuals vary
5- Heritable variation
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Observations
1.
Exponential fertility:
Organisms have the ability to produce such a large
number of offspring they would increase exponentially if
all organisms in the population reproduced.
2.
Stable Population Size:
The population of a organism is stable. It is neither
increasing or decreasing with the exception of seasonal
changes.
3.
Limited Resources:
There are not enough environmental resources for all,
the
organisms must compete for available resources.
4.
Individual Variation:
Individuals have different traits and phenotypes.
5.
Heritable Variation:
The phenotypic traits and variation is inherited by
offspring.
Descent with Modification
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3 Inferences:
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1- Struggle for existence
2- Non-random survival
3- Natural selection
(differential success in
reproduction)
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Inferences
1.
Struggle for existence:
Organisms fight to survive through competition
for resources (ex: food, shelter, predators,
etc.)
2.
Non-random mating:
Those that are the most fit are the most likely
to mate
3.
Natural selection:
Predators, nature, etc. select those that are
better suited to the environment leading to a
gradual change toward favorable
characteristics .
Achieving Descent with
Modification
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Artificial Selection: an external force
selects which mating events occur
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Occurs in domesticated plants and animals
How Mendel discovered genetics
How animals produce greater amounts of
milk, etc.
Natural Selection: random mating
events
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The effects of predator/prey relationships
Mates chosen upon organisms will
Artificial Selection
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Animals:
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Humans have used artificial selection
to create specific types of animal food
products
Plants:
Humans have used artificial selection
to produce more resilient plants
 Plants produced through artificial
selection include hybrid plants
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Natural Selection
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Predator/Prey relationships:
Predators determine which organisms are
the most fit
 Organisms that are the most able to avoid
predators, find food, shelter, etc. survive to
reproduce
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Environmental factors:
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Availability of food and shelter, as well as
weather determines which organisms
survive to preproduce
Evolution evidence:
Biogeography
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Geographical
distribution of species
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Physical barriers such
as lakes, rivers,
mountains, oceans,
etc.
Examples:
Islands vs. Mainland
Australia
Continents
Evolution evidence:
The Fossil Record
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Succession of
forms over time
Transitional links
Vertebrate descent
Evolution evidence:
Comparative Anatomy
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Homologous
structures
(homology)
Descent from a
common ancestor
Vestigial organs
Ex: whale/snake
hindlimbs; wings on
flightless birds
Evolution evidence:
Comparative
Embryology
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Pharyngeal
pouches, ‘tails’ as
embryos
Comparative Embryology
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Evolutionary evidence:
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Embryology : the study of embryonic
development; comparison of the development of fetal
development
Scientists compare the development
of various organisms to determine
how similar the organisms are
 Similarity in embryonic development
suggests evolutionary links
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Evolution evidence:
Molecular Biology
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Similarities in DNA,
proteins, genes,
and gene products
Common genetic
code
Final words…...
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“Absence of
evidence is not
evidence of
absence.”
Lecture #2
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Chapter 23~
The Evolution of
Populations
Population genetics
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Population:
a localized group of individuals
belonging to the same species
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Species:
a group of populations whose
individuals have the potential to
interbreed and produce fertile
offspring
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Gene pool:
the total aggregate of genes in
a population at any one time
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Population genetics:
the study of genetic changes in
populations
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Modern synthesis/neo-Darwinism:
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formed in the 1940’s it states that the population
is the unit of evolution and natural selection has
significant role as the most important mechanism
“Individuals are selected, but populations
evolve.”
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The selection of individuals in a population allows
certain traits to be passed from one generation to
the next and the overall population changes
Hardy-Weinberg Theorem
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Serves as a model for the
genetic structure of a
nonevolving population
(equilibrium)
5 conditions:
1- Very large population
size
2- No migration
3- No net mutations
4- Random mating
5- No natural selection
Hardy-Weinberg Theorem
1.
Very large population size
In small populations, genetic drift can can alter allele
frequencies
2.
No migration
There must be no transfer of alleles between two
populations
3.
No net mutations
A mutation alters the gene pool
4.
Random mating
The selection of mates for particular characteristics does
not allow for the necessary random mating
5.
No natural selection
Differential survival and selection favor the transmission
of some alleles but not others
Hardy-Weinberg Equation
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p=frequency of one allele (A)
q=frequency of the other allele (a);
p+q=1.0
(p=1-q & q=1-p)
P2=frequency of AA genotype
2pq=frequency of Aa plus aA genotype
q2=frequency of aa genotype;
p 2 + 2pq + q 2 = 1.0
Microevolution, I
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A change in the
gene pool of a
population over a
succession of
generations
Genetic drift:
changes in the gene
pool of a small
population due to
chance (usually
reduces genetic
variability)
Microevolution, II
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The Bottleneck
Effect: type of genetic
drift resulting from a
reduction in population
such that the surviving
population is no longer
genetically
representative of the
original population
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Usually a result of
natural disaster
Microevolution, III
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Founder Effect:
a cause of genetic
drift attributable to
colonization by a
limited number of
individuals from a
parent population
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Seen on the various
Galapagos Islands
Microevolution, IV
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Gene Flow:
genetic exchange
due to the
migration of fertile
individuals or
gametes between
populations
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reduces
differences
between
populations
Microevolution, V
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Mutations:
a change in an
organism’s DNA
(gametes; many
generations);
original source of
genetic variation
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raw material for
natural selection
Microevolution, VI
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Nonrandom mating:
inbreeding and
assortive mating
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both shift
frequencies of
different
genotypes
Selection for
specific
characteristics
Microevolution, VII
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Natural Selection:
differential success
in reproduction;
only form of
microevolution that
adapts a population
to its environment
Population variation
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Polymorphism:
coexistence of 2 or
more distinct forms of
individuals (morphs)
within the same
population
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Geographical
variation: differences
in genetic structure
between populations
(cline)
Variation preservation
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Prevention of natural
selection’s reduction of
variation
Diploidy
2nd set of chromosomes
hides variation in the
heterozygote
Balanced polymorphism
1- heterozygote advantage:
hybrid vigor
i.e., malaria/sickle-cell anemia
2- frequency dependent
selection: survival &
reproduction of any 1 morph
declines if it becomes too
common
Natural selection
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Fitness:
contribution an
individual makes
to the gene pool of
the next
generation
3 types:
A. Directional
B. Diversifying
C. Stabilizing
Natural selection
1.
Directional Selection
Shifts the overall makeup of the population to favor one
extreme or the other
Ex: Dark snails are selected over light or medium snails
2.
Diversifying Selection
Selection favors both extreme over the intermediate
individuals.
Ex: Light and Dark snails are selected over the medium
3.
Stabilizing Selection
The intermediate phenotype is selected over either of the
extremes
Ex: The medium snail is selected over the light or the dark
snail
Sexual selection
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Sexual dimorphism:
secondary sex
characteristic distinction
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Ex: Physical size or
plumage
Sexual selection:
selection towards
secondary sex
characteristics that leads
to sexual reproduction
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Ex: The use of feathers
to attract a mate
“Perfect” Organisms
Organisms are locked into historical
constraints.
2. Adaptations are often compromises.
3. Not all evolution is adaptive.
4. Selection can only edit variation that
exists.
- Evolution cannot create perfect
organisms
1.
Lecture #3
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Chapter 24 ~ The
Origin of Species
Macroevolution: the origin of new taxonomic groups
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Speciation: the origin of new species
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1- Anagenesis (phyletic evolution): accumulation of
heritable changes
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2- Cladogenesis (branching evolution): budding of
new species from a parent species that continues to
exist (basis of biological diversity)
What is a species?
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Biological species concept (Mayr):
a population or group of populations whose
members have the potential to interbreed
and produce viable, fertile offspring (genetic
exchange is possible and that is genetically
isolated from other populations)
Reproductive Isolation (isolation of gene pools), I
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Prezygotic barriers: impede mating between
species or hinder the fertilization of the ova
Habitat (snakes; water/terrestrial)
Behavioral (fireflies; mate signaling)
Temporal (salmon; seasonal mating)
Mechanical (flowers; pollination anatomy)
Gametic (frogs; egg coat receptors)
Reproductive Isolation, II
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Postzygotic barriers: fertilization occurs, but the hybrid
zygote does not develop into a viable, fertile adult
Reduced hybrid viability (frogs; zygotes fail to
develop or reach sexual maturity)
Reduced hybrid fertility (mule; horse x donkey;
cannot backbreed)
Hybrid breakdown (cotton; 2nd generation hybrids
are sterile)
Modes of speciation
on how gene flow is interrupted)
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Allopatric:
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Sympatric:
populations
segregated by a geographical
barrier; can result in adaptive
radiation (island species)
reproductively isolated
subpopulation in the midst of
its parent population (change in
genome); polyploidy in plants;
cichlid fishes
(based
Adaptive Radiation
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Adaptation from a common ancestor
when placed into varied ecological
systems.
Caused by migration
 New ecological niches
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Examples of Adaptive
Radiation
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Hawaii – Hawaiian archipelago illustrates
diversity and adaptation
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Kauai: oldest and most humid island
Maui: some vegetation grows even on dry
side
Hawaii: active volcano, very dry, very wet
side of island
Most organisms are found only on the
archipelago
Punctuated equilibria
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Tempo of speciation:
gradual vs.
divergence in rapid bursts; Niles
Eldredge and Stephen Jay Gould
(1972); helped explain the non-gradual
appearance of species in the fossil
record
Punctuated equilibria
Species change most as they arise
from ancestral species
 Relatively little change occurs after
 Eldredge & Gould’s model contrasts
with the model of gradualism
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Growth & Development
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Heterochrony: change in the rate or timing of
developmental events
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Can change physical features as well as timing of
reproductive development
Allometric Growth: Proportioning that helps
give a body its specific form
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Small changes in these rates changes the adult
form substantially
Evolution Continued
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Evolution is not goal oriented
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Bushes do not grow toward only one point,
organisms do not evolve along a single lineage.
Speciation creates several branches, many which
become extinct
The species that survives the longest and
produces the most offspring determines the
direction of major evolutionary trends “Species
Selection”
Lecture #4
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Chapter 25 ~
Phylogeny &
Systematics
Phylogeny:
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the evolutionary history of a species
Systematics:
the study of biological
diversity in an evolutionary
context
The fossil record:
the
ordered array of fossils,
within layers, or strata, of
sedimentary rock
Paleontologists
The fossil record
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Sedimentary rock: rock formed from sand and
mud that once settled on the bottom of seas,
lakes, and marshes
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Dating:
1- Relative ~ geologic time scale; sequence of
species
2- Absolute ~ radiometric dating; age using
half-lives of radioactive isotopes
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Homology vs. Analogy
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Homology – similar characteristics due to
common ancestry
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Hawaiian silversword plants
Analogy – similar characteristics due to
environmental pressures and natural
selection
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Australian and North American burrowing
moles
Biogeography: the study of the past and
present distribution of species
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Pangaea-250 mya
Permian extinction
Geographic isolation-180 mya
African/South American
reptile fossil similarities
Australian marsupials
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Mass extinction
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Permian
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Cretaceous
(250
million years ago): 90% of
marine animals; Pangea
merge
(65
million years ago): death of
dinosaurs, 50% of marine
species; low angle comet
Phylogenetics
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The tracing of evolutionary
relationships
(phylogenetic tree)
Linnaeus
Binomial
Genus, specific epithet
Homo sapiens
Taxon (taxa)
Phylogenetic Trees
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Cladistic Analysis: taxonomic approach
that classifies organisms according to
the order in time at which branches
arise along a phylogenetic tree
(cladogram)
Clade: each evolutionary branch in a
cladogram
Types:
1- Monophyletic single ancestor that
gives rise to all species in that taxon
and to no species in any other taxon;
legitimate cladogram
Phylogenetic Trees
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2- Polyphyletic members of a
taxa are derived from 2 or more
ancestral forms not common to all
members; does not meet cladistic
criterion
3- Paraphyletic lacks the
common ancestor that would
unite the species; does not meet
cladistic criterion
Constructing a Cladogram
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Sorting homology vs. analogy...
Homology:
likenesses attributed to
common ancestry
Analogy:
likenesses attributed to similar ecological
roles and natural selection
Convergent evolution:
species from
different evolutionary branches that
resemble one another due to similar
ecological roles
A Cladogram
Phylogram
Branch length – represents the
number of changes that have taken
place (DNA Sequence)
 The greater the length the greater the
change in the DNA
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Ultrametric Trees
All organisms from a common
ancestor have survived for the same
number of years
 Equal chronological amounts of time
are represented by equal lengths on
the tree
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Phylogeny as Hypothesis
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Phylogenic Trees give rise to evolutionary
hypotheses
Using maximum parsimony and maximum
likelihood, scientists develop evolutionary
hypotheses
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Occam’s razor
Assumptions
Molecular comparison
Genomes
Orthologous genes – homologous
genes in different gene pools due to
speciation
 Paralogous genes – gene duplication
creating multiple copies in the same
genome
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Genome Evolution
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Orthologous genes are widespread
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50% of genes are traceably orthologous between
humans and yeast
Paralogous genes do not appear at the same
rate as phenotypic complexity
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Humans have 5x as many genes as yeast despite
complexity differences
Universal Tree of life
1960’s – DNA is universal in all
organisms, therefore, all organisms
must have a common ancestor
 DNA identifies branching patterns
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Region must be sequenced
 Must have evolved slowly
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Universal Tree
Common Ancestor
Unknown Organism
Bacteria
Prokaryotes
Most bacteria known today
Archaea
Prokaryotes
Varied Environments
Eukarya
Plants, Fungi and Animals
Single Celled Organisms
Contain True Nuclei