Download Biology: Concepts and Connections, Fifth Edition

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Clown, Fool, or Simply Well Adapted?
 The blue-footed booby has many
specialized characteristics that are very
functional in water but less useful on
land
 Such evolutionary adaptations are
inherited traits that enhance an
organism's ability to survive and
reproduce in its particular environment
 Evolution is the changes in organisms
over time
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PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Webbing
Romero
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No webbing
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A sea voyage helped Darwin frame his theory of
evolution
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Pre-Darwinian ideas about the origin of species
 Early Greek philosophers: Simpler life forms
preceded more complex ones
 Aristotle: Species are fixed and do not evolve;
had a great impact on Western thinking
 Judeo-Christian biblical view: All species
were individually designed by a divine
creator
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In the century prior to Darwin, only a
few scientists questioned the belief that
species are fixed
 Buffon: The study of fossils suggested
that Earth is older than 6,000 years, and
fossil forms might be early versions of
modern forms
 Lamarck: Fossils are related to modern
forms because life evolves; acquired
characteristics are inherited
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Charles Darwin made a round-the-world sea
voyage as a naturalist on HMS Beagle in the
1830s
 Darwin observed similarities between living
and fossil organisms and the diversity of life
on the Galápagos Islands
 Darwin's experiences during the voyage
helped him frame his ideas about evolution
 Lyell's Principles of Geology led him to realize
that still-operating natural forces gradually
change EarthPOP GEN & EVOL LECTURE 1
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Great
Britain
Europe
Asia
North
America
PACIFIC
OCEAN
The
Galápagos
Islands
PACIFIC
OCEAN
Pinta
Marchena
Pinzón
Isabela
0
0
40 km
Equator
Daphne
Islands
Santa Santa
Cruz Fe
Florenza
Africa
San
Cristobal
PACIFIC
OCEAN
Equator
South
America
Genovesa
Santiago
Fernandina
ATLANTIC
OCEAN
Australia
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Tasmania
New
Zealand
Española
40 miles
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After his return, Darwin began to
document his observations and his new
theory of evolution
 Alfred Wallace conceived a theory
almost identical to Darwin's; both
works were presented to the scientific
community
 Darwin's On the Origin of Species by
Means of Natural Selection was published
in 1859
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"Descent with modification" summarizes
Darwin's view of life
 All organisms are related through descent
from a remote common ancestor
 Descendants spread into diverse habitats
over millions of years and acquired
adaptations to their environments
 The history of life resembles a tree with
multiple branchings from a common trunk
 Species that are closely related share
characteristics
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Darwin proposed natural selection as the
mechanism of evolution
 The essence of Darwin's theory of natural
selection is differential success in reproduction
 Organisms produce more offspring than the
environment can support
 Organisms vary in many characteristics that
can be inherited
 Excessive numbers of organisms lead to a
struggle for survival
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 Individuals whose characteristics are best
adapted to their environment are more likely
to survive and reproduce
 The unequal ability of individuals to survive
and reproduce leads to a gradual change in
the characteristics of a population over
generations
 Natural selection is supported by evidence
from artificial selection
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African wild dog
Coyote
Wolf
Fox
Jackal
Thousands to
millions of years
of natural selection
Ancestral canine
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The study of fossils provides strong evidence for
evolution
 Fossils are the hard parts of organisms that
remain after organic materials decay
 Rarely, an entire organism is fossilized
 The fossil record strongly supports the theory
of evolution
 Changes in sea level and drying and refilling
of lakes over time result in rock strata that
trap organisms
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 Fossils appear in an ordered array
within layers of sedimentary rocks
 The fossil record reveals that organisms
have evolved in a historical sequence
 Many fossils link early extinct species
with species living today
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A mass of other evidence reinforces the
evolutionary view of life
 Biogeography
 The geographic distribution of species
suggested to Darwin that organisms
evolve from common ancestors
 Isolated organisms resemble each other
more than organisms in similar but
distant places
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Comparative anatomy
 Homologous structures are features
that often have different functions but
are structurally similar because of
common ancestry
 Vestigial structures are remnants of
structures that served important
functions in an organism's ancestors
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Human
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Cat
Whale
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Bat
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 Comparative
embryology
 Common embryonic
structures in all vertebrates
are evidence for common
descent
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Pharyngeal
pouches
Post-anal
tail
Chick embryo
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Human embryo
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 Molecular
biology
 Comparisons of DNA and amino
acid sequences between different
organisms reveal evolutionary
relationships
 Molecular biology provides strong
evidence that all life forms are
related
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Scientists can observe natural selection in
action
 Examples of evolutionary adaptation
observed over a short time
 Different camouflage adaptations in
different environments
 Development of pesticide resistance in
insects
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Chromosome with gene
conferring resistance
to pesticide
Additional
applications of the
same pesticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
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Pesticide application
Survivor
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Examples of evolutionary adaptation
reveal three key points about natural
selection
 Natural selection is more of an editing
process than a creative mechanism
 Natural selection is contingent on time
and place
 Significant evolutionary change can
occur in a short time
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13.6 Populations are the units of evolution
 Population
 A group of individuals of the same species living in the same
place at the same time
 May be isolated from other groups or concentrated
 The smallest unit that can evolve
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Population genetics
 Combines Darwin's and Mendel's ideas
in studying how populations change
genetically over time
 The modern synthesis
 Connects population genetics with
other sciences
 Focuses on population as the unit of
evolution and central role of natural
selection
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Studying evolution at the population level
 Evolution: change in the prevalence of
certain heritable characteristics in a
population over a span of generations
 Gene pool: the total collection of genes in a
population at any one time
 Microevolution: a change in the relative
frequencies of alleles in a gene pool
 Species: a group of populations capable of
interbreeding and producing fertile
offspring
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The gene pool of a nonevolving population
remains constant over the generations
 In a nonevolving population, the
shuffling of alleles that accompanies
sexual reproduction does not alter the
genetic makeup of the population
 In Hardy-Weinberg equilibrium, the
frequency of each allele in the gene pool
will remain constant unless acted upon
by other agents
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For a population to be in HardyWeinberg equilibrium, it must satisfy
five main conditions
 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
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The Hardy-Weinberg conditions are
rarely met in nature
 We can follow alleles in a population to
observe if Hardy-Weinberg equilibrium
exists
 Hardy-Weinberg equilibrium provides
a basis for understanding how
populations evolve
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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)
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In addition to natural selection, genetic drift and
gene flow can contribute to evolution
 Genetic drift: change in the gene pool of a
population due to chance
 Can alter allele frequencies in a population
 The smaller the population, the greater the
impact
 Bottleneck effect: an event that drastically
reduces population size
 Founder effect: colonization of a new
location by a small number of individuals
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Original
population
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Bottlenecking
event
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Surviving
population
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Gene flow: the movement of individuals
or gametes between populations
 Can alter allele frequencies in a
population
 Tends to reduce differences between
populations
 Natural selection
 Best-adapted individuals have the most
reproductive success
 Results in accumulation of traits that
adapt a population to its environment

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Endangered species often have
reduced variation
 Loss of genetic variability due to
bottlenecking may reduce a
population's ability to adapt to
environmental change
 Particularly threatening to
endangered species such as the
cheetah
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Variation is extensive in most populations
 Individual variation exists in all sexually
reproducing populations
 Heritable variation results from a combination
of genotype and environmental influences
 Polymorphism: two or more forms of
phenotypic characteristics
 Geographic variation: variation of an
inherited characteristic from place to place
 May occur along a geographic continuum (a
cline)
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Mutation and sexual recombination generate
variation
 Mutations-changes in the nucleotide sequence
of DNA-can create new alleles
 Only mutations in cells that produce gametes
can affect a population's gene pool
 A mutation may rarely improve adaptation to
the environment and thus contribute to
evolution
 Sexual recombination generates variation by
shuffling
alleles
meiosis
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A1
Parents
A2
A1
A3

Meiosis
A1
A2
A3
Gametes
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A1
A2
A3
Gametes
Fertilization
Offspring,
with new
combinations
of alleles
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A1
A1
A2
A3
and
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The evolution of antibiotic resistance in
bacteria is a serious public health concern
 Natural selection has led to the evolution
of antibiotic-resistant bacteria
 Overuse and misuse of antibiotics has
contributed to the proliferation of
antibiotic-resistant strains
 Example: tuberculosis
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Diploidy and balancing selection
preserve variation
 Diploidy (two sets of chromosomes)
helps to prevent populations from
becoming genetically uniform
 Recessive alleles are "hidden" from
natural selection and remain in the
population
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Balancing selection allows two or more
phenotypic forms in a population
 Balanced polymorphism may result from
 Heterozygote advantage; example: sicklecell disease
 Frequency-dependent selection
 Neutral variation provides no apparent
advantage or disadvantage
 Example: fingerprints

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The perpetuation of genes defines
evolutionary fitness
 Evolutionary fitness is the relative
contribution an individual makes to the
gene pool of the next generation
 Survival of genes depends on production of
fertile offspring
 Selection indirectly adapts a population to
its environment by acting on phenotype
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Natural selection can alter variation in a
population in three ways
 Stabilizing selection: favors intermediate
phenotypes
 Directional selection: acts against
individuals at one of the phenotypic
extremes
 Disruptive selection: favors individuals
at both extremes of the phenotypic range
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Frequency of individuals
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
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Directional selection
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Disruptive selection
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Sexual selection may produce sexual
dimorphism
 Sexual dimorphism
 The distinction in appearance between
males and females of a species
 Sexual selection
 The determining of "who mates with
whom"
 Leads to the evolution of secondary sexual
characteristics that may give individuals
an advantage in mating
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Natural selection cannot fashion perfect
organisms
 There are at least four reasons why natural
selection cannot produce perfection
 Organisms are limited by historical
constraints
 Adaptations are often compromises
 Chance and natural selection interact
 Selection can only edit existing variations
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