Download Chapter 11 Evolution of Populations

Section 3 Examples of Evolution
Objectives
• Identify four elements in the process of natural
selection
• Describe how natural selection has affected the
bacteria that cause tuberculosis
• Relate natural selection to the beak size of
finches
• Summarize the process of species formation
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Section 2 How Populations Evolve
Objectives
• Identify the Hardy-Weinberg principle
• Describe the five forces that cause genetic
change in a population
• Identify why selection against unfavorable
recessive traits is slow
• Contrast directional and stabilizing selection
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New Vocabulary
Section 13-3
• Divergence
• Speciation
• Subspecies
Section 15-2
• Hardy-Weinberg principle
• Gene flow
• Nonrandom mating
• Genetic drift
• Normal distribution
• Directional selection
• Stabilizing selection
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Section 3 Examples of Evolution
Natural Selection at Work
• The process of natural selection is driven by four important
points that are true for all real populations:
1. All populations have genetic ____________________.
variation
2. The environment presents _____________________
to
challenges
successful reproduction.
more offspring than the
3. Individuals tend to produce ________
environment can support.
4. Individuals that are ___________
better able to cope with the
challenges presented by their environment tend to leave more
offspring than those individuals less suited to the
environment do.
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Section 3 Examples of Evolution
Natural Selection
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• In some instances, natural selection can be observed
in ___________
periods of time
short
– When small organisms with short life spans, like
bacteria
insects
_____________
or _____________
become
resistant to ______________
or ______________
antibiotics
insecticide
– When organisms are exposed to different
environments
_______________
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Section 3 Examples of Evolution
Antibiotic Resistance
•
The lung disease tuberculosis (TB) is caused by the
bacterium _________________
_______________.
Mycobacterium
tuberculosis
•
antibiotics
In the 1950s, two effective _________________,
isoniazid and rifampin, became available to treat TB.
•
1980s however, _______
new strains of
In the late _______,
M. tuberculosis that are largely or completely
resistant
_______________
to isoniazid and rifampin
appeared….
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Section 3 Examples of Evolution
Evolution of Antibiotic Resistance
• Rifampin normally kills bacteria cells by binding to
RNA polymerase, which will prevent
transcription
______________
• However, TB bacteria began passing on a
mutation
________________
that prevents rifampin from
binding to the polymerase.
• So, TB bacteria with the mutation were able to
survive
_____________
treatment with the antibiotic, leading
to the evolution of rifampin resistance in M.
tuberculosis.
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Section 3 Examples of Evolution
Evolution in Darwin’s Finches
• Darwin collected 31 specimens of finches from three
___________
when he visited the Galápagos
islands
Islands.
• All in all, he collected nine different species that were
all very similar except for their _________
beaks
• Darwin suggested that they all evolved from an
original _______________
species that changed as
common
different populations accumulated adaptations to
food
different ____________
sources.
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Section 3 Examples of Evolution
25
• A study of the finches was carried out over ____
years beginning in 1973 by Peter and Rosemary
Grant
____________
of Princeton University.
• They discovered that during drier years, birds with
stout
__________
beaks survived better because they
could eat ___________
hard/dry seeds…
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Section 3 Examples of Evolution
• But during ______
years, birds with ___________
wet
slender
beaks survived just as well because the seeds are
softer
______________
• So the beaks of bird populations did
evolve
available
______________
in response to the ___________
food supply
Average Beak Size
versus Year
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Section 3 Examples of Evolution
Formation of New Species
• The formation of new
species, called
speciation
_________________,
occurs in ___________.
stages
• The accumulation of
differences between
groups is called
divergence
_________________.
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Adaptive Radiation
• When an original ancestor has diverged into many
different species over time, the ancestor has gone
through a special type of divergence, called
adaptive
radiation
______________
______________
• Example…Darwin’s finches
original ancestor
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Chapter 13
Section 3 Examples of Evolution
Forming Subspecies
• Divergence occurs as populations of the same
genetically
species differ _______________
because of
conditions
adaptations to different living ______________
– This leads to the evolution of _______________,
subspecies
interbreed
which can still ________________,
but they
represent the first steps towards speciation
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• Remember, separate species cannot interbreed….
– This might mean that they…
• ______________
cannot mate
physically
viable
• Do not produce _____________
offspring
• Are isolated because they have different
____________
seasons
mating
infertile
• Produce ______________
offspring
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• Example….
– The offspring of a donkey and a horse is called a
mule
____________
sterile
• This hybrid offspring is _____________,
so
donkeys and horses are considered separate
species
• Example…
– A similar situation applies to lions and tigers
• The offspring of a male lion and female tiger is
liger
called a __________
• The offspring of a male tiger and female lion is
called a ______________
tigon
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• The male hybrids are ________________,
infertile
so ligers
cannot interbreed with other ligers, as tigons cannot
interbreed with other tigons, so lions and tigers
separate
remain classified as ________________
species
• Furthermore, tigers and lions do not live in the same
_____________
so they don’t reproduce together
habitats
_______________
naturally
ligers
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Hardy-Weinberg Principle
• After studying Mendel’s work regarding genetics,
scientists wondered if dominant traits would randomly
or ________________
spontaneously replace recessive alleles in a
population
• In 1908, an English mathematician named G. H.
Hardy
_____________
and a German physician named
Weinberg devised a mathematical
Wilhelm ______________
equation that allows us to keep track of the
alleles
________________
in a population
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p2 + 2pq + q2 = 1
dominant alleles
p2 = frequency of homozygous _____________
2pq = frequency of _________________
heterozygotes
recessive allele
q2 = frequency of homozygous ______________
*****All of the frequencies must add up to _____
1
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p2 + 2pq + q2 = 1
• So, for example, the frequency of individuals with
cystic fibrosis (cc) is 0.00048
– In the equation above, where would this number
be plugged in?
q2
– Then, you can determine the rest of the
mathematically
frequencies __________________
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• Hardy and Weinberg determined that allele
frequencies do _____
not change from population to
population, unless the population is acted on by a
process that ____________
particular alleles
favors
• So for example, a lethal dominant allele does not
become more ____________
just because it is
common
dominant
• This discovery, called the Hardy-Weinberg
______________,
states that allele frequencies do
principle
not change unless ___________________
forces act
evolutionary
on a population
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• Five evolutionary forces frequently act upon the all of
the genes in a population called a gene _______
pool
• These forces are…
mutations
– _________________
– _________________
Gene flow
Nonrandom mating
– _________________
Genetic drift
– _________________
Natural selection
– _________________
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Mutations
• Mutations in _____
DNA affect the codons in mRNA
produced during ________________
transcription
• Recall, however, that several codons code for the
same amino acid, so not all mutations affect
_____________
synthesis
protein
• Mutations rates in populations are usually very
slow
______________,
but they still provide new variation
in a population
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Gene Flow
migration
• Gene flow is the movement or ______________
of
alleles into or out of a population
enter
– Immigration = new alleles ___________
a
population
– Emigration = alleles ____________
leave
a population
• Example…
– If tall individuals leave a population, what kind of
alleles will be left?
short
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Nonrandom Mating
• Nonrandom mating occurs when organisms
chose their mates based on certain
____________
traits
• In animals, for example, females often select
males based on their….
– __________
size
– __________
color
food
– Ability to gather ________
or provide
_____________
shelter
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• Female widowbirds prefer
males with ________
tails
long
• How will this change the
alleles for tail length over
time?
long tail alleles will become
more common
Widowbird
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Genetic Drift
• Occurs when the allelic frequencies in a population
are altered by __________
chance events
• The effects of genetic drift are seen more often in
small
_______________
populations because their gene
pool is _______________
smaller
• Example…
– Imagine that there is a bird population containing
90 red birds and 10 white birds…
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• A hurricane blows 10 birds off of the mainland which
end up on an island….
3 of these birds are red and _____
7
– ____
are white
– Due to chance, the allele frequencies of the 10
___________
“founder” birds of the new island population
are drastically different from birds on the mainland
– This type of genetic drift is often called the
________________
founder
effect
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Natural Selection
• Favorable traits are caused by genes, but natural
selection acts upon the __________
which is a
trait
phenotype
• So, for example, natural selection cannot eliminate a
______________
disease like cystic fibrosis,
recessive
because heterozygous carriers have the same
______________________
as homozygous
phenotype
dominant individuals
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• There are also different __________
types
of natural
selection that affect gene pools differently
– ________________
selection
directional
stabilizing
– ________________
selection
– Disruptive selection
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Directional Selection
• Selects for _____
one extreme version of a trait, so the
population is said to be moving in one ___________
direction
• Example….Why might woodpeckers with long beaks
be selected for?
They reach more food in trees
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Stabilizing Selection
• Occurs when individuals with ____________
average
variations of a trait are selected for
• Example…spider size
big
– Birds prefer to eat _____________
spiders
– Small spiders do not __________
prey well
hunt
average
– ______________
sized spiders survive the best
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Disruptive selection
• Where both
extremes of a trait
are selected for and
the average is
selected against
• Can lead to
speciation over time
Why might very large beaks or very small beaks
be an advantage over medium sized beaks?
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Section 3 Examples of Evolution
Objective 1
• Identify four elements in the process of natural
selection
– ___________________
of offspring
Overproduction
– ________________
variation
Genetic
– ________________
to survive
Struggle
– ________________
Differential
reproduction
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Section 3 Examples of Evolution
Objective 2
• Describe how natural selection has affected the
bacteria that cause tuberculosis
Bacteria resistant to antibiotics
are selected for
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Section 3 Examples of Evolution
Objective 3
• Relate natural selection to the beak size of
finches…
• Which type of beak enabled survival in dry
environments
stout
• Did beak type affect survival during
wet/rainy years?
no
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Section 3 Examples of Evolution
Objective 4
• Summarize the process of species formation…
– What is different about subspecies versus
separate species?
Subspecies may still interbreed
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Section 2 How Populations Evolve
Objective 5
• Identify the Hardy-Weinberg principle…
Allele frequencies do not change unless
___________________
forces act on a population
evolutionary
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Section 2 How Populations Evolve
Objective 6
• Describe the five forces that cause genetic
change in a population
– Mutations
affect protein synthesis, usually slow
– Gene flow alleles migrate into or out of a population
– Nonrandom mating Mates are picked due to
certain traits
– Genetic Drift Chance events affect gene pools
– Natural Selection Selects for favorable traits,
Directional, disruptive,
or stabilizing
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Section 2 How Populations Evolve
Objective 7
• Identify why selection against unfavorable
recessive traits is slow
Because natural selection acts on phenotypes,
so heterozygous individuals still pass on recessive
alleles
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Section 2 How Populations Evolve
Objective 8
• Contrast directional and stabilizing and disruptive
selection
Selects for one
extreme of a trait
Selects for both
extremes of a trait
and can lead to
speciation
Selects for average
forms of a trait
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