Transcript Biology - Ms. Rago's Class Website

Ch. 16 Evolution of Populations
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• Microevolution = gradual change in a population
overtime
• Speciation = the origin of new species, is at the focal
point of evolution
• Macroevolution = evolutionary change on a grand
(LARGE) scale
- Replacement of one species with another
- Increases biodiversity
Figure 14.1
What is a species?
Carolus Linnaeus - Swedish physician and botanist, used
physical characteristics to distinguish species and developed
the binomial system of naming organisms
Scientific name = the genus and species names;
Should be italicized or underlined
Homo sapiens
»Homo = genus
»sapien = species
Linnaeus’ system established the basis for taxonomy, the
branch of biology concerned with naming and classifying the
diverse forms of life
Similarities between some species and
variation within a species can make
defining species difficult.
Different
species!
SAME
species!
Species: A population or group of
populations whose members can
interbreed and produce fertile offspring
NOT the
SAME
SPECIES!
LIGER
Scientific Name: Panthera leo × Panthera tigris
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Variation and Gene Pools
A population is a group of individuals of the
same species that interbreed.
A gene pool consists of all genes, including all the
different alleles, that are present in a population.
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Variation and Gene Pools
Gene Pool for Fur Color in Mice
Sample Population
Frequency of Alleles
allele for
brown fur
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allele for
black fur
16-216-2
Evolution
Evolution
as Genetic
as Genetic
Change
Change
• Evolution is any change over time in
the relative frequencies of alleles in
a population.
• Populations, not individual
organisms, can evolve over time.
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Possible effects to a population of mice due to
natural selection
Frequency of
individuals
Original
population
Original
population
Figure 13.16
Evolved
population
Stabilizing selection
Phenotypes (fur color)
Directional selection
Disruptive selection
What type of selection is this???
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What is genetic drift?
• A random change in allele frequency is called
genetic drift.
Bottleneck Effect
Founder Effect
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Genetic Drift
Founder Effect- genetic drift when a small group of
individuals colonizes a new habitat and allele
frequencies shift
The new population will be genetically different from
the parent population.
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Genetic Drift
Bottleneck effect – a form of genetic drift causing
a shift in allele frequencies due to a drastic event
(earthquake, volcano, etc.)
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Evolution Versus Genetic Equilibrium
• The Hardy-Weinberg principle states that allele
frequencies in a population will remain constant
unless one or more factors cause those
frequencies to change.
• When allele frequencies remain constant it is
called genetic equilibrium.
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Evolution Versus Genetic
Equilibrium
Five conditions are required to maintain genetic
equilibrium from generation to generation:
1.
Random mating (no sexual selection)
2.
Very large population
3.
No movement into or out of the population
4.
No mutations
5.
No natural selection
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The Process of
Speciation
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16-3 The Process of Speciation
Natural selection and chance events can change
the relative frequencies of alleles in a population
Speciation = formation of NEW species!
Figure 14.1
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Isolating Mechanisms
What factors are involved in the formation of
new species?
The gene pools of two populations must become
separated for them to become new species =
isolating mechanisms
• When populations become reproductively isolated
from each other, they cannot interbreed and
produce fertile offspring.
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Isolating Mechanisms
Reproductive isolation can develop in a variety of
ways, including:
• behavioral isolation
• geographic isolation
• temporal isolation
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Isolating Mechanisms
Behavioral Isolation - populations are capable of
interbreeding but have differences in courtship
rituals or other reproductive strategies that involve
behavior.
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MECHANISMS OF SPECIATION (the “HOW”)
Geographic isolation – separation by geographic
barriers
A. harrisi
A. leucurus
Isolating Mechanisms
Temporal isolation - when two or more species
reproduce at different times.
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How did speciation in the Galápagos
finches occur?
By the :
• founding of a new population
• geographic isolation
• changes in new population's
gene pool
• reproductive isolation
• ecological competition
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Speciation in Darwin's Finches
Founders Arrive
A few finches—
species A—travel
from South
America to one of
the Galápagos
Islands.
There, they
survive and
reproduce.
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Speciation in Darwin's Finches
Geographic Isolation
Some birds from
species A cross
to a second
island.
The two
populations no
longer share a
gene pool.
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Speciation in Darwin's Finches
Changes in the Gene Pool
Seed sizes on the
second island
favor birds with
large beaks.
The population
on the second
island evolves
into population
B, with larger
beaks.
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Speciation in Darwin's Finches
Reproductive Isolation
• If population B birds cross back to the first island,
they will not mate with birds from population A.
• Populations A and B are separate species.
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Speciation in Darwin's Finches
Ecological Competition
• As species A and B compete for available seeds
on the first island, they continue to evolve in a
way that increases the differences between them.
• A new species—C—may evolve.
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