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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 13
How Populations Evolve
Modules 13.4 – 13.12
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
DARWIN’S THEORY AND THE MODERN
SYNTHESIS
13.4 Darwin proposed natural selection as the
mechanism of evolution
• Darwin observed that
– organisms produce more offspring than the
environment can support
– organisms vary in many characteristics
– these variations can be inherited
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Darwin concluded that individuals best suited
for a particular environment are more likely to
survive and reproduce than those less well
adapted
• Darwin saw natural selection as the basic
mechanism of evolution
– As a result, the proportion of individuals with
favorable characteristics increases
– Populations gradually change in response to the
environment
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Darwin also saw that when
humans choose organisms
with specific characteristics as
breeding stock, they are
performing the role of the
environment
– This is called artificial
selection
– Example of artificial
selection in plants: five
vegetables derived from
wild mustard
Figure 13.4A
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– Example of artificial selection in animals: dog
breeding
German shepherd
Yorkshire terrier
English springer
spaniel
Mini-dachshund
Golden retriever
Hundreds to
thousands of years
of breeding
(artificial selection)
Ancestral dog
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Figure 13.4B
• These five canine species evolved from a
common ancestor through natural selection
African wild
dog
Coyote
Fox
Wolf
Jackal
Thousands to
millions of years
of natural selection
Ancestral canine
Figure 13.4C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.5 Connection: Scientists can observe natural
selection in action
• Evolutionary adaptations have been observed
in populations of birds, insects, and many other
organisms
– Example: camouflage adaptations of mantids
that live in different environments
Figure 13.5A
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• The evolution of insecticide resistance is an
example of natural selection in action
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Figure 13.5B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.6 Populations are the units of evolution
• A species is a group of populations whose
individuals can interbreed and produce fertile
offspring
– Human populations tend
to concentrate locally, as
this satellite photograph
of North America shows
• The modern synthesis
connects Darwin’s theory
of natural selection with
population genetics
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 13.6
13.7 Microevolution is change in a population’s
gene pool over time
• A gene pool is the total collection of genes in a
population at any one time
• Microevolution is a change in the relative
frequencies of alleles in a gene pool
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13.8 The gene pool of a nonevolving population
remains constant over the generations
• Hardy-Weinberg equilibrium
states that the shuffling of
genes during sexual
reproduction does not alter
the proportions of different
alleles in a gene pool
– To test this, let’s look at an
imaginary, nonevolving
population of blue-footed
boobies
Webbing
No webbing
Figure 13.8A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• We can follow alleles in a population to observe
if Hardy-Weinberg equilibrium exists
Phenotypes
Genotypes
WW
Ww
ww
Number of animals
(total = 500)
320
160
20
Genotype frequencies
320/
500
= 0.64
Number of alleles
in gene pool
(total = 1,000)
640 W
Allele frequencies
800/
1,000
160/
500
20/
= 0.32
160 W + 160 w
= 0.8 W
200/
1,000
500
= 0.04
40 w
= 0.2 w
Figure 13.8B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Recombination
of alleles from
parent generation
SPERM
EGGS
WW
p2 = 0.64
WW
qp = 0.16
Ww
pq = 0.16
ww
q2 = 0.04
Next generation:
Genotype frequencies
0.64 WW
Allele frequencies
0.32 Ww
0.8 W
0.04 ww
0.2 w
Figure 13.8C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.9 Connection: The Hardy-Weinberg equation is
useful in public health science
• Public health scientists use the Hardy-Weinberg
equation to estimate frequencies of diseasecausing alleles in the human population
– Example: phenylketonuria (PKU)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.10 Five conditions are required for HardyWeinberg equilibrium
• The population is very large
• The population is isolated
• Mutations do not alter the gene pool
• Mating is random
• All individuals are equal in reproductive success
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.11 There are several potential causes of
microevolution
• Genetic drift is
a change in a
gene pool due
to chance
– Genetic drift
can cause the
bottleneck
effect
Original
population
Bottlenecking
event
Surviving
population
Figure 13.11A
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– or the founder effect
Figure 13.11B, C
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• Gene flow can change a gene pool due to the
movement of genes into or out of a population
• Mutation changes alleles
• Natural selection leads to differential
reproductive success
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.12 Adaptive change results when natural
selection upsets genetic equilibrium
• Natural selection results in the accumulation of
traits that adapt a population to its environment
– If the environment should change, natural
selection would favor traits adapted to the new
conditions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings