Download How natural selection affects variation

BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 13
How Populations Evolve
Modules 13.13 – 13.22
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
VARIATION AND NATURAL SELECTION
13.13 Variation is extensive in most populations
• Phenotypic variation may be environmental or
genetic in origin
– But only genetic changes result in evolutionary
adaptation
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• Many populations exhibit polymorphism and
geographic variation
Figure 13.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.14 Connection: Mutation and sexual
recombination generate variation
A1
Parents
A1
A2
A3
MEIOSIS
A1
A2
A3
Gametes
FERTILIZATION
Offspring,
with new
combinations
of alleles
A1
A2
A1
A3
and
Figure 13.14
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13.15 Overview: How natural selection affects
variation
• Natural selection tends to reduce variability in
populations
– The diploid condition preserves variation by
“hiding” recessive alleles
– Balanced polymorphism may result from the
heterozygote advantage
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.16 Not all genetic variation may be subject to
natural selection
• Some variations may be neutral, providing no
apparent advantage or disadvantage
– Example: human fingerprints
Figure 13.16
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13.17 Connection: Endangered species often have
reduced variation
• Low genetic variability may reduce the capacity
of endangered species to survive as humans
continue to alter the environment
– Studies have shown that cheetah populations
exhibit extreme genetic uniformity
– Thus they may have a
reduced capacity to
adapt to environmental
challenges
Figure 13.17
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.18 The perpetuation of genes defines
evolutionary fitness
• An individual’s Darwinian fitness is the
contribution it makes to the gene pool of the
next generation relative to the contribution
made by other individuals
• Production of fertile offspring is the only score
that counts in natural selection
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.19 There are three general outcomes of natural
selection
Frequency of
individuals
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.20 Sexual selection may produce sexual
dimorphism
• Sexual selection leads to the evolution of
secondary sexual characteristics
– These may give individuals an advantage in
mating
Figure 13.20A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.21 Natural selection cannot fashion perfect
organisms
• This is due to:
– historical constraints
– adaptive compromises
– chance events
– availability of variations
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
13.22 Connection: The evolution of antibiotic
resistance in bacteria is a serious public
health concern
• The excessive use of antibiotics is leading to the
evolution of antibiotic-resistant bacteria
– Example:
Mycobacterium
tuberculosis
Figure 13.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings