Transcript MECHANISMS OF EVOLUTION

MECHANISMS OF
EVOLUTION
CHAPTER 15.2
I. POPULATION GENETICS AND
EVOLUTION
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A. Populations, Not Individuals Evolve
Evolution occurs as a populations genes and their
frequencies change over time
Gene pool: all of a populations genes
Allelic frequency: the percentage of any specific
allele in a gene pool
Genetic equilibrium: when the frequency of a
populations allele remains the same over time
Calculating Allelic Frequency
First generation
Phenotype
frequency
Allele
frequency
White = 0
R’ = 0.25
Pink = 0.5
R = 0.75
Red = 0.5
Second generation
Phenotype
frequency
Allele
frequency
White = 0.125
R = 0.75
Pink = 0.25
R’ = 0.25
Red = 0.625
I. POPULATION GENETICS AND
EVOLUTION
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B. Changes in Genetic Equilibrium
Population in G.E. is NOT evolving
You must disrupt G.E. for a population to evolve
Things that can disrupt G.E.
 Mutations
 Environmental
 Chemicals
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factors
or radiation exposure
Genetic drift: the alteration of allelic frequencies
by chance events
I. POPULATION GENETICS AND
EVOLUTION
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B. Changes in Genetic Equilibrium
Genetic equilibrium also disrupted by immigration
and emigration
 Which
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is “into”? Which is “out of”?
Gene flow: the transport of genes by migrating
individuals
I. POPULATION GENETICS AND
EVOLUTION
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C. Natural Selection Acts on Variations
3 DIFFERENT TYPES OF NATURAL SELECTION
 Stabilizing
Selection
 Directional Selection
 Disruptive Selection
I. POPULATION GENETICS AND
EVOLUTION
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C. Natural Selection Acts on Variations
1. Stabilizing Selection:
 Favors
the “average” individual in a population
Selection for
average size
spiders
Normal
variation
I. POPULATION GENETICS AND
EVOLUTION
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C. Natural Selection Acts on Variations
2. Directional Selection:
 Favors
“one direction or the other direction”
Normal
variation
Selection
for longer
beaks
I. POPULATION GENETICS AND
EVOLUTION
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C. Natural Selection Acts on Variations
3. Disruptive Selection:
 Favors
“both directions”
Selection for
light limpets
Normal
variation
Selection for
dark limpets
I. POPULATION GENETICS AND
EVOLUTION
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C. Natural Selection Acts on Variations
All of these types of natural selection will favor one
specific trait in a species
This selection can lead to the “evolution of a new
species”
II. THE EVOLUTION OF SPECIES
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Speciation: the evolution of a new species
 Occurs
when members of a similar population can no
longer interbreed and produce fertile offspring
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A. Physical Barriers that Can Prevent
Interbreeding
Geographic isolation: occurs whenever a physical
barrier separates a species
 Can
be a land barrier or an ocean barrier
 New species evolve when G.I. occurs
II. THE EVOLUTION OF SPECIES
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B. Reproductive Isolation can Result in Speciation
Reproductive isolation: occurs when formerly
interbreeding organisms can no longer mate and
produce fertile offspring (P.F.O.)
C. A Change in Chromosome Numbers and
Speciation
Polyploid: any individual or species with a multiple
of the normal set of chromosomes
 Results from an error in “meiosis”
II. THE EVOLUTION OF SPECIES
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D. Speciation Rates
Gradualism: is the idea that species originate
through a “gradual” change over time.
Punctuated equilibrium: argues that speciation
occurs relatively quickly, in rapid bursts, with long
periods of genetic equilibrium in between.
 due
to: environmental changes and introduction of new
species into an environment
III. PATTERNS OF EVOLUTION
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A. Diversity in New Environments
2 types of evolution associated with being moved to
a new environment
 Adaptive
radiation
 Divergent evolution
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1. Adaptive Radiation:
 When
ancestral species evolve into an array of species
to fit a number of diverse habitats
 Darwin’s study on “finches” *(a type of bird; he
compared the shapes of their beaks)*
III. PATTERNS OF EVOLUTION
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A. Diversity in New Environments
2. Divergent Evolution:
 Is
s type of “adaptive radiation”
 Is a pattern of evolution in which similar species diverge
and become increasingly distinct/different.
 Occurs when a population changes as they adapt to
different environments
III. PATTERNS OF EVOLUTION
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B. Different Species can Look Alike
Convergent evolution: a pattern of evolution
where distantly related organisms evolve similar
traits/characteristics
Occurs when unrelated species occupy similar
environments
Polar bear and a “Snowy Owl” or “White Fox”
TODAYS ASSIGNMENT
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Pg. 133 #1-4
Pg. 137 #1-4
Pg. 142 #1-4
Pg. 146 #1-3
Pg. 147 #1-6
Should be a total of 21 questions
Turn in to me before you leave
HOMEWORK
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Due tomorrow as soon as you walk in the door.
Pg 1
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Pg. 83
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Pg 117
 1-10