Download Evolution

Warm Up
Describe natural selection and how
this leads to evolution.
•What is a mechanism?
Mechanisms of Evolution
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Natural Selection
Population Genetics
Genetic Drift
Gene Flow
Nonrandom mating
Mutation
Evolution
Natural Selection
Population Genetics
 Individuals in a population show variations.
 Variations can be inherited.
 Organisms have more offspring than can survive on
available resources.
 Variations that increase reproductive success will
have a greater chance of being passed on.
Natural Selection
 Acts to select the individuals that are best adapted
for survival and reproduction.
 Acts on an organisms phenotype and change allele
frequencies.
Allele Frequencies
Types of Natural Selection
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Stabilizing Selection
Directional Selection
Disruptive Selection
Sexual Selection
Evolution
Types of Natural Selection
 Stabilizing selection
 average phenotype has the highest fitness
 eliminates extreme phenotypes
Evolution
Types of Natural Selection
 Directional selection
 One Extreme phenotype has the highest
fitness
 Selection in one direction makes an
organism more fit.
Evolution
Types of Natural Selection
 Disruptive selection
 Splits population into two groups.
 Extreme phenotypes have higher fitness than
the average phenotype
Evolution
Types of Natural Selection
 Sexual selection
 In populations where males and females
differ significantly in appearance.
Sexual Selection
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Fitness
Fitness
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Reprodution
Survival
Reprodution
Survival
 Qualities of sexual attractiveness appear to be the
opposite of qualities that might enhance survival.
Evolution
Natural Selection
• Stabilizing Selection
• Directional Selection
• Disruptive Selection
Evolution
Genetic Drift
 A change in the allele frequencies in a
population that is due to chance
 Greater in smaller populations
 Greater Chance of losing an allele
Evolution
Genetic Drift
Small Population (Genetic Drift)
Genetic Drift
• Founder Effect
• Bottleneck
Evolution
Genetic Drift
Founder Effect
 small part of a population settles in a location
separated from the rest of the population
 Alleles that were uncommon in the original
population might be common in the new
population.
GeneticEvolution
Drift
Bottleneck
 Occurs when:
 population declines to a very low
number
 then rebounds
GeneticEvolution
Drift
Bottleneck
Population
Decreases
Why could less
diversity be bad?
The Survivors
Repopulate
What is Different?
Less Diversity
Evolution
Gene Flow
 Increases genetic variation within a population
 reduces differences between populations
Evolution
Nonrandom Mating
 Promotes inbreeding
 could lead to a change in allele proportions
favoring individuals that are homozygous for
particular traits
Chapter 15
Evolution
15.3 Shaping Evolutionary Theory
Gene Flow
 Increases genetic variation within a population
and reduces differences between populations
Nonrandom Mating
 Promotes inbreeding and could lead to a
change in allelic proportions favoring
individuals that are homozygous for
particular traits
Mutation
• Random change in genetic information
• Cause changes in allele frequencies
• Some advantageous
Speciation
• Species diverge
• Can occur due to isolation
• Become two separate species that cannot
reproduce
• Allopatric speciation
• Sympatric speciation
Isolation
• Reproductive Isolation
– gene Flow is prevented between two populations
of the same species.
– different mating seasons
Isolation
• Geographic Isolation
– A population that becomes divided (isolated) by a
physical barrier
– Each groups evolves differently
Chapter 15
Evolution
Abert squirrel
Kaibab squirrel
Evolution
Allopatric Speciation
Sympatric Speciation
 A physical barrier divides
one population into two or
more populations.
 A species evolves
into a new species
without a physical
barrier.
Chapter 15
Evolution
Chapter Diagnostic
Questions
Which is not a principle of Darwin’s theory about
the origin of species?
A. Individuals show variations.
B. Variations can be inherited.
C. Organisms have more offspring than
available resources will support.
D. Offspring always inherit the best traits.
Chapter 15
Evolution
15.3 Formative Questions
Which description is evidence that a
speciation has taken place?
Chapter 15
Evolution
15.3 Formative Questions
A. A physical barrier has caused two groups from a
population to adapt to different environments.
B. Some members can no longer produce fertile
offspring with members of the original population.
C. A small group has developed mating behaviors that
are different than those of the rest of the population.
D. Some members from a population have developed
physical characteristics that are different than the
original population.
Chapter 15
Evolution
Standardized Test Practice
Within a population of squirrels, those that
live higher in the mountains where it is
cooler have long fur. Squirrels that live in
the foothills where it is warmer have short
fur. The original population is believed to
have had intermediate fur length. Which
graph represents this type of natural
selection?
Chapter 15
Evolution
Standardized Test Practice
B.
A.
C.
Contrast the four types of natural
selection.