SlideShare ist ein Scribd-Unternehmen logo
1 von 50
LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures by
Erin Barley
Kathleen Fitzpatrick
The Evolution of Populations
Chapter 23
Overview: The Smallest Unit of Evolution
• One misconception is that organisms evolve
during their lifetimes
• Natural selection acts on individuals, but only
populations evolve
© 2011 Pearson Education, Inc.
• Variation in heritable traits is a prerequisite for
evolution
• Mendel’s work on pea plants provided evidence
of discrete heritable units (genes)
• Genetic variation among individuals is caused
by differences in genes or other DNA segments
• Phenotype is the product of inherited genotype
and environmental influences
• Natural selection can only act on variation with
a genetic component
Genetic variation makes evolution possible
© 2011 Pearson Education, Inc.
Mutation and sexual recombination produce the
variation that makes evolution possible
• Two processes, mutation and sexual
recombination, produce the variation in gene
pools that contributes to differences among
individuals
Mutation
• Mutations are changes in the nucleotide
sequence of DNA
• Mutations cause new genes and alleles to arise
Sexual Recombination
• Sexual recombination is far more important
than mutation in producing the genetic
differences that make adaptation possible
• This is particularly true with plants and animals,
but clearly isn’t as important in microbes, who
don’t have sex and can obtain genes through
lateral gene transfer (transformation)
• In addition, bacteria have the highest mutation
rates, so it contributes more to genetic
differences in them
• Microevolution is a change in allele
frequencies in a population over generations
• Three mechanisms cause allele frequency
change:
– Natural selection
– Genetic drift
– Gene flow
• Only natural selection causes adaptive
evolution
© 2011 Pearson Education, Inc.
Gene Pools and Allele Frequencies
• A population is a localized group of individuals
capable of interbreeding and producing fertile
offspring
• A gene pool consists of all the alleles for all loci
in a population
• A locus is fixed if all individuals in a population
are homozygous for the same allele
© 2011 Pearson Education, Inc.
Figure 23.6
Porcupine herd
Beaufort Sea
Porcupine
herd range
Fortymile
herd range
Fortymile herd
NORTHW
EST
TERRITORIES
ALASKA
CANADA
MAP
AREA
ALASKA
YUKON
• The frequency of an allele in a population can
be calculated
– For diploid organisms, the total number of
alleles at a locus is the total number of
individuals times 2
– The total number of dominant alleles at a locus
is 2 alleles for each homozygous dominant
individual plus 1 allele for each heterozygous
individual; the same logic applies for recessive
alleles
© 2011 Pearson Education, Inc.
• By convention, if there are 2 alleles at a locus,
p and q are used to represent their
frequencies
• The frequency of all alleles in a population will
add up to 1
– For example, p + q = 1
© 2011 Pearson Education, Inc.
• For example, consider a population of
wildflowers that is incompletely dominant for
color:
– 320 red flowers (CR
CR
)
– 160 pink flowers (CR
CW
)
– 20 white flowers (CW
CW
)
• Calculate the number of copies of each allele:
– CR
= (320 × 2) + 160 = 800
– CW
= (20 × 2) + 160 = 200
© 2011 Pearson Education, Inc.
• To calculate the frequency of each allele:
– p = freq CR
= 800 / (800 + 200) = 0.8
– q = freq CW
= 200 / (800 + 200) = 0.2
• The sum of alleles is always 1
– 0.8 + 0.2 = 1
© 2011 Pearson Education, Inc.
The Hardy-Weinberg Principle
• The Hardy-Weinberg principle describes a
population that is not evolving
• If a population does not meet the criteria of
the Hardy-Weinberg principle, it can be
concluded that the population is evolving
© 2011 Pearson Education, Inc.
Hardy-Weinberg Equilibrium
• The Hardy-Weinberg principle states that
frequencies of alleles and genotypes in a
population remain constant from generation to
generation if only Mendelian segregation and
recombination of alleles are at work
• In a given population where gametes contribute
to the next generation randomly, allele
frequencies will not change
• Mendelian inheritance preserves genetic
variation in a population
© 2011 Pearson Education, Inc.
LE 14-10
Red
CR
CR
Gametes
P Generation
CR
CW
White
CW
CW
Pink
CR
CW
CRGametes CW
F1 Generation
F2 Generation Eggs
CR
CW
CR
CR
CR
CR
CW
CR
CW
CW
CW
CW
Sperm
1
2
1
2
1
2
1
2
1
2
1
2
LE 23-4
Generation
3 25% CR
CR
Generation
4
50% CR
CW 25% CW
CW
50% CW
gametes
50% CR
come together at random
25% CR
CR
50% CR
CW 25% CW
CW
Alleles segregate, and subsequent
generations also have three types
of flowers in the same proportions
gametes
Generation
2
Generation
1
CR
CR
CW
CW
genotypegenotype
Plants mate
All CR
CW
(all pink flowers)
50% CR 50% CW
gametes gametes
come together at random
X
• If p and q represent the relative frequencies of
the only two possible alleles in a population at
a particular locus, then
– p2
+ 2pq + q2
= 1
– where p2
and q2
represent the frequencies of
the homozygous genotypes and 2pq
represents the frequency of the heterozygous
genotype
© 2011 Pearson Education, Inc.
Conditions for Hardy-Weinberg Equilibrium
• The Hardy-Weinberg theorem describes a hypothetical
population that is not evolving
• In real populations, allele and genotype frequencies do
change over time
• There are 5 conditions that must be met in order to have a
nonevolving population:
– 1. No natural selection
– 2. Extremely large population size
– 3. No gene flow
– 4. No mutations
– 5. Random mating
• If any of these processes occur, microevolution will occur
© 2011 Pearson Education, Inc.
• Three major factors alter allele frequencies and
bring about most evolutionary change:
– Natural selection
– Genetic drift
– Gene flow
Natural selection, genetic drift, and gene
flow can alter allele frequencies in a
population
© 2011 Pearson Education, Inc.
Natural Selection and Microevolution:
Darwin’s Finches
• Peter and Rosemary Grant have been
doing research on finches in the
Galapagos Islands since 1973
• They captured and tagged all of the birds
on Daphne Major, an island where
conditions swing between wet and dry
years
• They measured the length, width, and
depth of the birds’ beaks
Galápagos
Islands
PACIFIC
OCEANPinta
40 miles
40 km0 Florenza
0
Fernandina
Marchena
Genovesa
Equator
Santiago
Daphne Islands
Pinzón
Española
Isabela Santa
Cruz
Santa
Fe San
Cristobal
Figure 13.3c
Darwin’s Finches
• When it’s wet, grasses grow and produce a lot of
small seeds
• When it’s dry, the grasses don’t grow and the
available seeds from other plants are larger
• Smaller beaked birds are unable to crack larger
seeds and perish
• The Grants found that average beak size
increased during dry seasons and decreased
during wet seasons
• Thus, microevolution occurs as the environment
selects for beak size
Figure 23.2
1976
(similar to the
prior 3 years)
1978
(after
drought)
Averagebeakdepth(mm)
10
9
8
0
(a) The large ground finch
Figure 13.11a
23 the evolution of populations
Genetic Drift
• The smaller a sample, the greater the chance of
deviation from a predicted result
• Genetic drift describes how allele frequencies
fluctuate unpredictably from one generation to the
next
• Genetic drift tends to reduce genetic variation
through losses of alleles
© 2011 Pearson Education, Inc.
Figure 23.9-3
5
plants
leave
off-
spring
Generation 1
p (frequency of CR
) = 0.7
q (frequency of CW
) = 0.3
CR
CR CR
CR
CR
CW
CW
CW CR
CR
CR
CW
CR
CR
CR
CW
CR
CR
CR
CW
CR
CR
CW
CW
CR
CW
CR
CR CW
CW
CR
CW
CW
CW
CR
CR
CR
CW
CR
CW
Generation 2
p = 0.5
q = 0.5
2
plants
leave
off-
spring
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
CR
Generation 3
p = 1.0
q = 0.0
The Founder Effect
• The founder effect occurs when a few
individuals become isolated from a larger
population
• Allele frequencies in the small founder
population can be different from those in the
larger parent population
© 2011 Pearson Education, Inc.
The Bottleneck Effect
• The bottleneck effect is a sudden reduction in
population size due to a change in the
environment
• The resulting gene pool may no longer be
reflective of the original population’s gene pool
• If the population remains small, it may be further
affected by genetic drift
© 2011 Pearson Education, Inc.
Figure 23.10-3
Original
population
Bottlenecking
event
Surviving
population
Effects of Genetic Drift: A Summary
1. Genetic drift is significant in small populations
2. Genetic drift causes allele frequencies to
change at random
3. Genetic drift can lead to a loss of genetic
variation within populations
4. Genetic drift can cause harmful alleles to
become fixed
© 2011 Pearson Education, Inc.
Gene Flow
• Gene flow consists of the movement of alleles
among populations
• Alleles can be transferred through the movement
of fertile individuals or gametes (for example,
pollen)
• Gene flow tends to reduce variation among
populations over time
© 2011 Pearson Education, Inc.
• Evolution by natural selection involves both
change and “sorting”
– New genetic variations arise by chance
– Beneficial alleles are “sorted” and favored by
natural selection
• Only natural selection consistently results in
adaptive evolution
Natural selection is the only mechanism that
consistently causes adaptive evolution
© 2011 Pearson Education, Inc.
A Closer Look at Natural Selection
• Natural selection brings about adaptive
evolution by acting on an organism’s
phenotype
• The phrases “struggle for existence” and
“survival of the fittest” are misleading as they
imply direct competition among individuals
• Reproductive success is generally more subtle
and depends on many factors
© 2011 Pearson Education, Inc.
• Relative fitness is the contribution an
individual makes to the gene pool of the next
generation, relative to the contributions of other
individuals
• Selection favors certain genotypes by acting on
the phenotypes of certain organisms
© 2011 Pearson Education, Inc.
Directional, Disruptive, and Stabilizing
Selection
• Three modes of selection:
– Directional selection favors individuals at one
end of the phenotypic range
– Disruptive selection favors individuals at both
extremes of the phenotypic range
– Stabilizing selection favors intermediate
variants and acts against extreme phenotypes
© 2011 Pearson Education, Inc.
Figure 23.13
Original population
Phenotypes (fur color)Frequencyof
individualsOriginal
population
Evolved
population
(a) Directional selection (b) Disruptive selection (c) Stabilizing selection
• Natural selection increases the frequencies of
alleles that enhance survival and reproduction
• Adaptive evolution occurs as the match between
an organism and its environment increases
• Because the environment can change, adaptive
evolution is a continuous process
© 2011 Pearson Education, Inc.
• Genetic drift and gene flow do not consistently
lead to adaptive evolution as they can increase
or decrease the match between an organism
and its environment
© 2011 Pearson Education, Inc.
Sexual Selection
• Sexual selection is natural selection for mating
success
• It can result in sexual dimorphism, marked
differences between the sexes in secondary
sexual characteristics
© 2011 Pearson Education, Inc.
Figure 23.15
• Intrasexual selection is competition among
individuals of one sex (often males) for mates
of the opposite sex
• Intersexual selection, often called mate
choice, occurs when individuals of one sex
(usually females) are choosy in selecting their
mates
• Male showiness due to mate choice can
increase a male’s chances of attracting a
female, while decreasing his chances of
survival
© 2011 Pearson Education, Inc.
Diploidy
• Diploidy maintains genetic variation in the form
of hidden recessive alleles
• Heterozygotes can carry recessive alleles that
are hidden from the effects of selection
© 2011 Pearson Education, Inc.
• Heterozygote advantage occurs when
heterozygotes have a higher fitness than do
both homozygotes
• Natural selection will tend to maintain two or
more alleles at that locus
• The sickle-cell allele causes mutations in
hemoglobin but also confers malaria resistance
Heterozygote Advantage
© 2011 Pearson Education, Inc.
Natural Selection and Microevolution:
Sickle-Cell Anemia
• A mutation in the gene for hemoglobin results
in sickle-cell anemia if an individual has 2
copies of the gene (one from each parent)
• Red blood cells form a sickle shape and are
ineffective at transporting oxygen
• They tend to clump together in joints, cause
pain, and may break (hence, the anemia)
• Death before reaching reproductive age is
quite likely
Sickle-Cell Anemia
• If sickle-cell disease often causes death, shouldn’t the
frequency of the allele in the human population
decrease?
• It should be selected against, but in areas of the world
with high malaria rates, the frequency of the allele
increases
• Tony Allison showed that the sickle-cell allele in
heterozygotes provides protection against malaria,
known as the heterozygote advantage
• The parasite that causes malaria invades red blood
cells (RBCs) but doesn’t do well in sickle-shaped cells,
and about half of a heterozygote’s RBCs will sickle
Sickle-Cell Anemia
• Thus, nature has selected for sickle-cell
anemia because it protects people from
the parasite that causes malaria
• A heterozygous baby born in an area with
a high incidence of malaria has a 26%
better chance of surviving their birth and
childhood than a baby that is homozygous
for normal hemoglobin
Figure 23.17
Distribution of
malaria caused by
Plasmodium falciparum
(a parasitic unicellular eukaryote)
Key
Frequencies of the
sickle-cell allele
0–2.5%
2.5–5.0%
5.0–7.5%
7.5–10.0%
10.0–12.5%
>12.5%
Why Natural Selection Cannot Fashion
Perfect Organisms
1. Selection can act only on existing variations
2. Evolution is limited by historical constraints
3. Adaptations are often compromises
4. Chance, natural selection, and the
environment interact
© 2011 Pearson Education, Inc.

Weitere ähnliche Inhalte

Was ist angesagt?

26 lecture phylogeny
26 lecture phylogeny26 lecture phylogeny
26 lecture phylogenyveneethmathew
 
14 mendel and the gene idea
14 mendel and the gene idea14 mendel and the gene idea
14 mendel and the gene ideakindarspirit
 
23 lecture evolution_populations
23 lecture evolution_populations23 lecture evolution_populations
23 lecture evolution_populationsveneethmathew
 
18 Regulation of Gene Expression
18 Regulation of Gene Expression18 Regulation of Gene Expression
18 Regulation of Gene Expressionkindarspirit
 
13 meiosis and sexual life cycles
13 meiosis and sexual life cycles13 meiosis and sexual life cycles
13 meiosis and sexual life cycleskindarspirit
 
17 - From Gene to Protein
17 - From Gene to Protein17 - From Gene to Protein
17 - From Gene to Proteinkindarspirit
 
Population ecology ch 53
Population ecology ch 53Population ecology ch 53
Population ecology ch 53MrJewett
 
22 lecture descent_with_modification
22 lecture descent_with_modification22 lecture descent_with_modification
22 lecture descent_with_modificationveneethmathew
 
Ch 13: Meiosis and Sexual Life Cycles
Ch 13: Meiosis and Sexual Life CyclesCh 13: Meiosis and Sexual Life Cycles
Ch 13: Meiosis and Sexual Life Cyclesveneethmathew
 
16 the molecular basis of inheritance
16 the molecular basis of inheritance16 the molecular basis of inheritance
16 the molecular basis of inheritancekindarspirit
 
Biology in Focus - Chapter 22
Biology in Focus - Chapter 22Biology in Focus - Chapter 22
Biology in Focus - Chapter 22mpattani
 
Biology in Focus - Chapter 12
Biology in Focus - Chapter 12Biology in Focus - Chapter 12
Biology in Focus - Chapter 12mpattani
 
Ap Chapter 24 The Origin Of Species
Ap Chapter 24 The Origin Of SpeciesAp Chapter 24 The Origin Of Species
Ap Chapter 24 The Origin Of Speciessmithbio
 
Biology in Focus - Chapter 43
Biology in Focus - Chapter 43 Biology in Focus - Chapter 43
Biology in Focus - Chapter 43 mpattani
 
Ch 17: From Gene to Protein
Ch 17: From Gene to Protein Ch 17: From Gene to Protein
Ch 17: From Gene to Protein veneethmathew
 
Biology in Focus - Chapter 11
Biology in Focus - Chapter 11Biology in Focus - Chapter 11
Biology in Focus - Chapter 11mpattani
 
Chapter52
Chapter52Chapter52
Chapter52uv5
 

Was ist angesagt? (20)

20 lecture biotech
20 lecture biotech20 lecture biotech
20 lecture biotech
 
26 lecture phylogeny
26 lecture phylogeny26 lecture phylogeny
26 lecture phylogeny
 
14 mendel and the gene idea
14 mendel and the gene idea14 mendel and the gene idea
14 mendel and the gene idea
 
23 lecture evolution_populations
23 lecture evolution_populations23 lecture evolution_populations
23 lecture evolution_populations
 
18 Regulation of Gene Expression
18 Regulation of Gene Expression18 Regulation of Gene Expression
18 Regulation of Gene Expression
 
13 meiosis and sexual life cycles
13 meiosis and sexual life cycles13 meiosis and sexual life cycles
13 meiosis and sexual life cycles
 
17 - From Gene to Protein
17 - From Gene to Protein17 - From Gene to Protein
17 - From Gene to Protein
 
Ch 12: Cell Cycle
Ch 12: Cell CycleCh 12: Cell Cycle
Ch 12: Cell Cycle
 
Population ecology ch 53
Population ecology ch 53Population ecology ch 53
Population ecology ch 53
 
22 lecture descent_with_modification
22 lecture descent_with_modification22 lecture descent_with_modification
22 lecture descent_with_modification
 
Ch 13: Meiosis and Sexual Life Cycles
Ch 13: Meiosis and Sexual Life CyclesCh 13: Meiosis and Sexual Life Cycles
Ch 13: Meiosis and Sexual Life Cycles
 
16 the molecular basis of inheritance
16 the molecular basis of inheritance16 the molecular basis of inheritance
16 the molecular basis of inheritance
 
Biology in Focus - Chapter 22
Biology in Focus - Chapter 22Biology in Focus - Chapter 22
Biology in Focus - Chapter 22
 
Biology in Focus - Chapter 12
Biology in Focus - Chapter 12Biology in Focus - Chapter 12
Biology in Focus - Chapter 12
 
Ap Chapter 24 The Origin Of Species
Ap Chapter 24 The Origin Of SpeciesAp Chapter 24 The Origin Of Species
Ap Chapter 24 The Origin Of Species
 
Biology in Focus - Chapter 43
Biology in Focus - Chapter 43 Biology in Focus - Chapter 43
Biology in Focus - Chapter 43
 
Ch 17: From Gene to Protein
Ch 17: From Gene to Protein Ch 17: From Gene to Protein
Ch 17: From Gene to Protein
 
Biology in Focus - Chapter 11
Biology in Focus - Chapter 11Biology in Focus - Chapter 11
Biology in Focus - Chapter 11
 
12 the cell cycle
12 the cell cycle12 the cell cycle
12 the cell cycle
 
Chapter52
Chapter52Chapter52
Chapter52
 

Andere mochten auch

Chapter22
Chapter22Chapter22
Chapter22May Mar
 
Bio 2 - Lab 2 Photos
Bio 2 - Lab 2 PhotosBio 2 - Lab 2 Photos
Bio 2 - Lab 2 Photoskindarspirit
 
Chapter23
Chapter23Chapter23
Chapter23May Mar
 
Biology in Focus - Chapter 21
Biology in Focus - Chapter 21Biology in Focus - Chapter 21
Biology in Focus - Chapter 21mpattani
 
Biology in Focus - Chapter 25
Biology in Focus - Chapter 25Biology in Focus - Chapter 25
Biology in Focus - Chapter 25mpattani
 
09 cellular respiration
09 cellular respiration09 cellular respiration
09 cellular respirationkindarspirit
 
Ap Chapter 21
Ap Chapter 21Ap Chapter 21
Ap Chapter 21smithbio
 
Enviromental, industrial micro
Enviromental, industrial microEnviromental, industrial micro
Enviromental, industrial microLani Manahan
 
Microevolution Changing Allele Frequencies
Microevolution Changing Allele FrequenciesMicroevolution Changing Allele Frequencies
Microevolution Changing Allele FrequenciesTauqeer Ahmad
 

Andere mochten auch (16)

Chapter22
Chapter22Chapter22
Chapter22
 
Bio 2 - Lab 2 Photos
Bio 2 - Lab 2 PhotosBio 2 - Lab 2 Photos
Bio 2 - Lab 2 Photos
 
19 - Viruses
19 - Viruses19 - Viruses
19 - Viruses
 
Chapter 22 Ppt
Chapter 22 PptChapter 22 Ppt
Chapter 22 Ppt
 
Chapter23
Chapter23Chapter23
Chapter23
 
Biology in Focus - Chapter 21
Biology in Focus - Chapter 21Biology in Focus - Chapter 21
Biology in Focus - Chapter 21
 
Biology in Focus - Chapter 25
Biology in Focus - Chapter 25Biology in Focus - Chapter 25
Biology in Focus - Chapter 25
 
09 cellular respiration
09 cellular respiration09 cellular respiration
09 cellular respiration
 
10 photosynthesis
10 photosynthesis10 photosynthesis
10 photosynthesis
 
54 lectures ppt
54 lectures ppt54 lectures ppt
54 lectures ppt
 
52 lectures ppt
52 lectures ppt52 lectures ppt
52 lectures ppt
 
53 lectures ppt
53 lectures ppt53 lectures ppt
53 lectures ppt
 
50 lectures ppt
50 lectures ppt50 lectures ppt
50 lectures ppt
 
Ap Chapter 21
Ap Chapter 21Ap Chapter 21
Ap Chapter 21
 
Enviromental, industrial micro
Enviromental, industrial microEnviromental, industrial micro
Enviromental, industrial micro
 
Microevolution Changing Allele Frequencies
Microevolution Changing Allele FrequenciesMicroevolution Changing Allele Frequencies
Microevolution Changing Allele Frequencies
 

Ähnlich wie 23 the evolution of populations

Biology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - Powerpoint Biology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - Powerpoint Mel Anthony Pepito
 
MDCAT/AKU/NUMS lecture unit= 17 Evolution.pptx
MDCAT/AKU/NUMS lecture unit= 17 Evolution.pptxMDCAT/AKU/NUMS lecture unit= 17 Evolution.pptx
MDCAT/AKU/NUMS lecture unit= 17 Evolution.pptxmudasirfsd333
 
chapter_19_powerpoint.pptx
chapter_19_powerpoint.pptxchapter_19_powerpoint.pptx
chapter_19_powerpoint.pptxbirhankassa
 
مشروووووع الوراثه
مشروووووع الوراثهمشروووووع الوراثه
مشروووووع الوراثهALaa Al-Assaf
 
Population Genetics_Dr. Ashwin Atkulwar
Population Genetics_Dr. Ashwin AtkulwarPopulation Genetics_Dr. Ashwin Atkulwar
Population Genetics_Dr. Ashwin AtkulwarAshwin Atkulwar
 
Ch 23_Evolution of Population.ppt
Ch 23_Evolution of Population.pptCh 23_Evolution of Population.ppt
Ch 23_Evolution of Population.pptYdemneYdemne
 
Biology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - PowerpointBiology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - PowerpointMr. Walajtys
 
Sources of variation in organic evolution
Sources of variation in organic evolutionSources of variation in organic evolution
Sources of variation in organic evolutionEkramuddin Md
 
23 lecture BIOL 1010-30 Gillette College
23 lecture BIOL 1010-30 Gillette College23 lecture BIOL 1010-30 Gillette College
23 lecture BIOL 1010-30 Gillette Collegedeskam2
 
Evolutionary Biology.ppt
Evolutionary Biology.pptEvolutionary Biology.ppt
Evolutionary Biology.pptTzlk
 
Evolution and gene frequencies my report
Evolution and gene frequencies my reportEvolution and gene frequencies my report
Evolution and gene frequencies my reportsembagot
 
POPULATION GENETICS
POPULATION GENETICS POPULATION GENETICS
POPULATION GENETICS Self-employed
 
Form 5 chapter 9-variation
Form 5 chapter 9-variationForm 5 chapter 9-variation
Form 5 chapter 9-variationBong Tong
 
Evidence of Evolution by Natural Selection - how basic evolutionary principal...
Evidence of Evolution by Natural Selection - how basic evolutionary principal...Evidence of Evolution by Natural Selection - how basic evolutionary principal...
Evidence of Evolution by Natural Selection - how basic evolutionary principal...Madison Elsaadi
 
Hardy – weinberg law
 Hardy – weinberg law Hardy – weinberg law
Hardy – weinberg lawShabnamkhan113
 

Ähnlich wie 23 the evolution of populations (20)

chap23 (1).ppt
chap23 (1).pptchap23 (1).ppt
chap23 (1).ppt
 
Biology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - Powerpoint Biology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - Powerpoint
 
What is evolution
What is evolutionWhat is evolution
What is evolution
 
MDCAT/AKU/NUMS lecture unit= 17 Evolution.pptx
MDCAT/AKU/NUMS lecture unit= 17 Evolution.pptxMDCAT/AKU/NUMS lecture unit= 17 Evolution.pptx
MDCAT/AKU/NUMS lecture unit= 17 Evolution.pptx
 
chapter_19_powerpoint.pptx
chapter_19_powerpoint.pptxchapter_19_powerpoint.pptx
chapter_19_powerpoint.pptx
 
مشروووووع الوراثه
مشروووووع الوراثهمشروووووع الوراثه
مشروووووع الوراثه
 
Population Genetics_Dr. Ashwin Atkulwar
Population Genetics_Dr. Ashwin AtkulwarPopulation Genetics_Dr. Ashwin Atkulwar
Population Genetics_Dr. Ashwin Atkulwar
 
Ch 23_Evolution of Population.ppt
Ch 23_Evolution of Population.pptCh 23_Evolution of Population.ppt
Ch 23_Evolution of Population.ppt
 
Biology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - PowerpointBiology - Chp 16 - Evolution Of Populations - Powerpoint
Biology - Chp 16 - Evolution Of Populations - Powerpoint
 
Sources of variation in organic evolution
Sources of variation in organic evolutionSources of variation in organic evolution
Sources of variation in organic evolution
 
23 lecture BIOL 1010-30 Gillette College
23 lecture BIOL 1010-30 Gillette College23 lecture BIOL 1010-30 Gillette College
23 lecture BIOL 1010-30 Gillette College
 
Evolutionary Biology.ppt
Evolutionary Biology.pptEvolutionary Biology.ppt
Evolutionary Biology.ppt
 
Evolution and gene frequencies my report
Evolution and gene frequencies my reportEvolution and gene frequencies my report
Evolution and gene frequencies my report
 
Microevolution
MicroevolutionMicroevolution
Microevolution
 
POPULATION GENETICS
POPULATION GENETICS POPULATION GENETICS
POPULATION GENETICS
 
Form 5 chapter 9-variation
Form 5 chapter 9-variationForm 5 chapter 9-variation
Form 5 chapter 9-variation
 
Arushi arora
Arushi aroraArushi arora
Arushi arora
 
Bio16 speciation
Bio16 speciationBio16 speciation
Bio16 speciation
 
Evidence of Evolution by Natural Selection - how basic evolutionary principal...
Evidence of Evolution by Natural Selection - how basic evolutionary principal...Evidence of Evolution by Natural Selection - how basic evolutionary principal...
Evidence of Evolution by Natural Selection - how basic evolutionary principal...
 
Hardy – weinberg law
 Hardy – weinberg law Hardy – weinberg law
Hardy – weinberg law
 

Mehr von kindarspirit

Bio 2 - Lab 1 Photos
Bio 2 - Lab 1 PhotosBio 2 - Lab 1 Photos
Bio 2 - Lab 1 Photoskindarspirit
 
15 the chromosomal basis of inheritance
15 the chromosomal basis of inheritance15 the chromosomal basis of inheritance
15 the chromosomal basis of inheritancekindarspirit
 
08 an introduction to metabolism
08 an introduction to metabolism08 an introduction to metabolism
08 an introduction to metabolismkindarspirit
 
07 membrane structure and function
07 membrane structure and function07 membrane structure and function
07 membrane structure and functionkindarspirit
 
06 a tour of the cell
06 a tour of the cell06 a tour of the cell
06 a tour of the cellkindarspirit
 
05 the structure and function of large biological molecules
05 the structure and function of large biological molecules05 the structure and function of large biological molecules
05 the structure and function of large biological moleculeskindarspirit
 
04 carbon and the molecular diversity of life
04 carbon and the molecular diversity of life04 carbon and the molecular diversity of life
04 carbon and the molecular diversity of lifekindarspirit
 
02 the chemical context of life
02 the chemical context of life02 the chemical context of life
02 the chemical context of lifekindarspirit
 
01 themes in the study of life
01 themes in the study of life01 themes in the study of life
01 themes in the study of lifekindarspirit
 

Mehr von kindarspirit (10)

Bio 2 - Lab 1 Photos
Bio 2 - Lab 1 PhotosBio 2 - Lab 1 Photos
Bio 2 - Lab 1 Photos
 
15 the chromosomal basis of inheritance
15 the chromosomal basis of inheritance15 the chromosomal basis of inheritance
15 the chromosomal basis of inheritance
 
08 an introduction to metabolism
08 an introduction to metabolism08 an introduction to metabolism
08 an introduction to metabolism
 
07 membrane structure and function
07 membrane structure and function07 membrane structure and function
07 membrane structure and function
 
06 a tour of the cell
06 a tour of the cell06 a tour of the cell
06 a tour of the cell
 
05 the structure and function of large biological molecules
05 the structure and function of large biological molecules05 the structure and function of large biological molecules
05 the structure and function of large biological molecules
 
04 carbon and the molecular diversity of life
04 carbon and the molecular diversity of life04 carbon and the molecular diversity of life
04 carbon and the molecular diversity of life
 
03 water and life
03 water and life03 water and life
03 water and life
 
02 the chemical context of life
02 the chemical context of life02 the chemical context of life
02 the chemical context of life
 
01 themes in the study of life
01 themes in the study of life01 themes in the study of life
01 themes in the study of life
 

Kürzlich hochgeladen

UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8DianaGray10
 
Introduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptxIntroduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptxMatsuo Lab
 
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPAAnypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPAshyamraj55
 
COMPUTER 10 Lesson 8 - Building a Website
COMPUTER 10 Lesson 8 - Building a WebsiteCOMPUTER 10 Lesson 8 - Building a Website
COMPUTER 10 Lesson 8 - Building a Websitedgelyza
 
Comparing Sidecar-less Service Mesh from Cilium and Istio
Comparing Sidecar-less Service Mesh from Cilium and IstioComparing Sidecar-less Service Mesh from Cilium and Istio
Comparing Sidecar-less Service Mesh from Cilium and IstioChristian Posta
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfinfogdgmi
 
Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™Adtran
 
COMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online CollaborationCOMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online Collaborationbruanjhuli
 
Building Your Own AI Instance (TBLC AI )
Building Your Own AI Instance (TBLC AI )Building Your Own AI Instance (TBLC AI )
Building Your Own AI Instance (TBLC AI )Brian Pichman
 
UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6DianaGray10
 
Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve Decarbonization
Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve DecarbonizationUsing IESVE for Loads, Sizing and Heat Pump Modeling to Achieve Decarbonization
Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve DecarbonizationIES VE
 
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...Aggregage
 
Computer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and HazardsComputer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and HazardsSeth Reyes
 
Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...
Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...
Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...DianaGray10
 
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019IES VE
 
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfJamie (Taka) Wang
 
VoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXVoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXTarek Kalaji
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Will Schroeder
 
Linked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesLinked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesDavid Newbury
 

Kürzlich hochgeladen (20)

UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8
 
Introduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptxIntroduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptx
 
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPAAnypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPA
 
COMPUTER 10 Lesson 8 - Building a Website
COMPUTER 10 Lesson 8 - Building a WebsiteCOMPUTER 10 Lesson 8 - Building a Website
COMPUTER 10 Lesson 8 - Building a Website
 
Comparing Sidecar-less Service Mesh from Cilium and Istio
Comparing Sidecar-less Service Mesh from Cilium and IstioComparing Sidecar-less Service Mesh from Cilium and Istio
Comparing Sidecar-less Service Mesh from Cilium and Istio
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdf
 
Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™Meet the new FSP 3000 M-Flex800™
Meet the new FSP 3000 M-Flex800™
 
COMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online CollaborationCOMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online Collaboration
 
Building Your Own AI Instance (TBLC AI )
Building Your Own AI Instance (TBLC AI )Building Your Own AI Instance (TBLC AI )
Building Your Own AI Instance (TBLC AI )
 
UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6
 
Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve Decarbonization
Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve DecarbonizationUsing IESVE for Loads, Sizing and Heat Pump Modeling to Achieve Decarbonization
Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve Decarbonization
 
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
The Data Metaverse: Unpacking the Roles, Use Cases, and Tech Trends in Data a...
 
Computer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and HazardsComputer 10: Lesson 10 - Online Crimes and Hazards
Computer 10: Lesson 10 - Online Crimes and Hazards
 
Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...
Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...
Connector Corner: Extending LLM automation use cases with UiPath GenAI connec...
 
20230104 - machine vision
20230104 - machine vision20230104 - machine vision
20230104 - machine vision
 
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
 
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
activity_diagram_combine_v4_20190827.pdfactivity_diagram_combine_v4_20190827.pdf
 
VoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXVoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBX
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
 
Linked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesLinked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond Ontologies
 

23 the evolution of populations

  • 1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick The Evolution of Populations Chapter 23
  • 2. Overview: The Smallest Unit of Evolution • One misconception is that organisms evolve during their lifetimes • Natural selection acts on individuals, but only populations evolve © 2011 Pearson Education, Inc.
  • 3. • Variation in heritable traits is a prerequisite for evolution • Mendel’s work on pea plants provided evidence of discrete heritable units (genes) • Genetic variation among individuals is caused by differences in genes or other DNA segments • Phenotype is the product of inherited genotype and environmental influences • Natural selection can only act on variation with a genetic component Genetic variation makes evolution possible © 2011 Pearson Education, Inc.
  • 4. Mutation and sexual recombination produce the variation that makes evolution possible • Two processes, mutation and sexual recombination, produce the variation in gene pools that contributes to differences among individuals
  • 5. Mutation • Mutations are changes in the nucleotide sequence of DNA • Mutations cause new genes and alleles to arise
  • 6. Sexual Recombination • Sexual recombination is far more important than mutation in producing the genetic differences that make adaptation possible • This is particularly true with plants and animals, but clearly isn’t as important in microbes, who don’t have sex and can obtain genes through lateral gene transfer (transformation) • In addition, bacteria have the highest mutation rates, so it contributes more to genetic differences in them
  • 7. • Microevolution is a change in allele frequencies in a population over generations • Three mechanisms cause allele frequency change: – Natural selection – Genetic drift – Gene flow • Only natural selection causes adaptive evolution © 2011 Pearson Education, Inc.
  • 8. Gene Pools and Allele Frequencies • A population is a localized group of individuals capable of interbreeding and producing fertile offspring • A gene pool consists of all the alleles for all loci in a population • A locus is fixed if all individuals in a population are homozygous for the same allele © 2011 Pearson Education, Inc.
  • 9. Figure 23.6 Porcupine herd Beaufort Sea Porcupine herd range Fortymile herd range Fortymile herd NORTHW EST TERRITORIES ALASKA CANADA MAP AREA ALASKA YUKON
  • 10. • The frequency of an allele in a population can be calculated – For diploid organisms, the total number of alleles at a locus is the total number of individuals times 2 – The total number of dominant alleles at a locus is 2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual; the same logic applies for recessive alleles © 2011 Pearson Education, Inc.
  • 11. • By convention, if there are 2 alleles at a locus, p and q are used to represent their frequencies • The frequency of all alleles in a population will add up to 1 – For example, p + q = 1 © 2011 Pearson Education, Inc.
  • 12. • For example, consider a population of wildflowers that is incompletely dominant for color: – 320 red flowers (CR CR ) – 160 pink flowers (CR CW ) – 20 white flowers (CW CW ) • Calculate the number of copies of each allele: – CR = (320 × 2) + 160 = 800 – CW = (20 × 2) + 160 = 200 © 2011 Pearson Education, Inc.
  • 13. • To calculate the frequency of each allele: – p = freq CR = 800 / (800 + 200) = 0.8 – q = freq CW = 200 / (800 + 200) = 0.2 • The sum of alleles is always 1 – 0.8 + 0.2 = 1 © 2011 Pearson Education, Inc.
  • 14. The Hardy-Weinberg Principle • The Hardy-Weinberg principle describes a population that is not evolving • If a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving © 2011 Pearson Education, Inc.
  • 15. Hardy-Weinberg Equilibrium • The Hardy-Weinberg principle states that frequencies of alleles and genotypes in a population remain constant from generation to generation if only Mendelian segregation and recombination of alleles are at work • In a given population where gametes contribute to the next generation randomly, allele frequencies will not change • Mendelian inheritance preserves genetic variation in a population © 2011 Pearson Education, Inc.
  • 16. LE 14-10 Red CR CR Gametes P Generation CR CW White CW CW Pink CR CW CRGametes CW F1 Generation F2 Generation Eggs CR CW CR CR CR CR CW CR CW CW CW CW Sperm 1 2 1 2 1 2 1 2 1 2 1 2
  • 17. LE 23-4 Generation 3 25% CR CR Generation 4 50% CR CW 25% CW CW 50% CW gametes 50% CR come together at random 25% CR CR 50% CR CW 25% CW CW Alleles segregate, and subsequent generations also have three types of flowers in the same proportions gametes Generation 2 Generation 1 CR CR CW CW genotypegenotype Plants mate All CR CW (all pink flowers) 50% CR 50% CW gametes gametes come together at random X
  • 18. • If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then – p2 + 2pq + q2 = 1 – where p2 and q2 represent the frequencies of the homozygous genotypes and 2pq represents the frequency of the heterozygous genotype © 2011 Pearson Education, Inc.
  • 19. Conditions for Hardy-Weinberg Equilibrium • The Hardy-Weinberg theorem describes a hypothetical population that is not evolving • In real populations, allele and genotype frequencies do change over time • There are 5 conditions that must be met in order to have a nonevolving population: – 1. No natural selection – 2. Extremely large population size – 3. No gene flow – 4. No mutations – 5. Random mating • If any of these processes occur, microevolution will occur © 2011 Pearson Education, Inc.
  • 20. • Three major factors alter allele frequencies and bring about most evolutionary change: – Natural selection – Genetic drift – Gene flow Natural selection, genetic drift, and gene flow can alter allele frequencies in a population © 2011 Pearson Education, Inc.
  • 21. Natural Selection and Microevolution: Darwin’s Finches • Peter and Rosemary Grant have been doing research on finches in the Galapagos Islands since 1973 • They captured and tagged all of the birds on Daphne Major, an island where conditions swing between wet and dry years • They measured the length, width, and depth of the birds’ beaks
  • 22. Galápagos Islands PACIFIC OCEANPinta 40 miles 40 km0 Florenza 0 Fernandina Marchena Genovesa Equator Santiago Daphne Islands Pinzón Española Isabela Santa Cruz Santa Fe San Cristobal Figure 13.3c
  • 23. Darwin’s Finches • When it’s wet, grasses grow and produce a lot of small seeds • When it’s dry, the grasses don’t grow and the available seeds from other plants are larger • Smaller beaked birds are unable to crack larger seeds and perish • The Grants found that average beak size increased during dry seasons and decreased during wet seasons • Thus, microevolution occurs as the environment selects for beak size
  • 24. Figure 23.2 1976 (similar to the prior 3 years) 1978 (after drought) Averagebeakdepth(mm) 10 9 8 0
  • 25. (a) The large ground finch Figure 13.11a
  • 27. Genetic Drift • The smaller a sample, the greater the chance of deviation from a predicted result • Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next • Genetic drift tends to reduce genetic variation through losses of alleles © 2011 Pearson Education, Inc.
  • 28. Figure 23.9-3 5 plants leave off- spring Generation 1 p (frequency of CR ) = 0.7 q (frequency of CW ) = 0.3 CR CR CR CR CR CW CW CW CR CR CR CW CR CR CR CW CR CR CR CW CR CR CW CW CR CW CR CR CW CW CR CW CW CW CR CR CR CW CR CW Generation 2 p = 0.5 q = 0.5 2 plants leave off- spring CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR CR Generation 3 p = 1.0 q = 0.0
  • 29. The Founder Effect • The founder effect occurs when a few individuals become isolated from a larger population • Allele frequencies in the small founder population can be different from those in the larger parent population © 2011 Pearson Education, Inc.
  • 30. The Bottleneck Effect • The bottleneck effect is a sudden reduction in population size due to a change in the environment • The resulting gene pool may no longer be reflective of the original population’s gene pool • If the population remains small, it may be further affected by genetic drift © 2011 Pearson Education, Inc.
  • 32. Effects of Genetic Drift: A Summary 1. Genetic drift is significant in small populations 2. Genetic drift causes allele frequencies to change at random 3. Genetic drift can lead to a loss of genetic variation within populations 4. Genetic drift can cause harmful alleles to become fixed © 2011 Pearson Education, Inc.
  • 33. Gene Flow • Gene flow consists of the movement of alleles among populations • Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) • Gene flow tends to reduce variation among populations over time © 2011 Pearson Education, Inc.
  • 34. • Evolution by natural selection involves both change and “sorting” – New genetic variations arise by chance – Beneficial alleles are “sorted” and favored by natural selection • Only natural selection consistently results in adaptive evolution Natural selection is the only mechanism that consistently causes adaptive evolution © 2011 Pearson Education, Inc.
  • 35. A Closer Look at Natural Selection • Natural selection brings about adaptive evolution by acting on an organism’s phenotype • The phrases “struggle for existence” and “survival of the fittest” are misleading as they imply direct competition among individuals • Reproductive success is generally more subtle and depends on many factors © 2011 Pearson Education, Inc.
  • 36. • Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals • Selection favors certain genotypes by acting on the phenotypes of certain organisms © 2011 Pearson Education, Inc.
  • 37. Directional, Disruptive, and Stabilizing Selection • Three modes of selection: – Directional selection favors individuals at one end of the phenotypic range – Disruptive selection favors individuals at both extremes of the phenotypic range – Stabilizing selection favors intermediate variants and acts against extreme phenotypes © 2011 Pearson Education, Inc.
  • 38. Figure 23.13 Original population Phenotypes (fur color)Frequencyof individualsOriginal population Evolved population (a) Directional selection (b) Disruptive selection (c) Stabilizing selection
  • 39. • Natural selection increases the frequencies of alleles that enhance survival and reproduction • Adaptive evolution occurs as the match between an organism and its environment increases • Because the environment can change, adaptive evolution is a continuous process © 2011 Pearson Education, Inc.
  • 40. • Genetic drift and gene flow do not consistently lead to adaptive evolution as they can increase or decrease the match between an organism and its environment © 2011 Pearson Education, Inc.
  • 41. Sexual Selection • Sexual selection is natural selection for mating success • It can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics © 2011 Pearson Education, Inc.
  • 43. • Intrasexual selection is competition among individuals of one sex (often males) for mates of the opposite sex • Intersexual selection, often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates • Male showiness due to mate choice can increase a male’s chances of attracting a female, while decreasing his chances of survival © 2011 Pearson Education, Inc.
  • 44. Diploidy • Diploidy maintains genetic variation in the form of hidden recessive alleles • Heterozygotes can carry recessive alleles that are hidden from the effects of selection © 2011 Pearson Education, Inc.
  • 45. • Heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes • Natural selection will tend to maintain two or more alleles at that locus • The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance Heterozygote Advantage © 2011 Pearson Education, Inc.
  • 46. Natural Selection and Microevolution: Sickle-Cell Anemia • A mutation in the gene for hemoglobin results in sickle-cell anemia if an individual has 2 copies of the gene (one from each parent) • Red blood cells form a sickle shape and are ineffective at transporting oxygen • They tend to clump together in joints, cause pain, and may break (hence, the anemia) • Death before reaching reproductive age is quite likely
  • 47. Sickle-Cell Anemia • If sickle-cell disease often causes death, shouldn’t the frequency of the allele in the human population decrease? • It should be selected against, but in areas of the world with high malaria rates, the frequency of the allele increases • Tony Allison showed that the sickle-cell allele in heterozygotes provides protection against malaria, known as the heterozygote advantage • The parasite that causes malaria invades red blood cells (RBCs) but doesn’t do well in sickle-shaped cells, and about half of a heterozygote’s RBCs will sickle
  • 48. Sickle-Cell Anemia • Thus, nature has selected for sickle-cell anemia because it protects people from the parasite that causes malaria • A heterozygous baby born in an area with a high incidence of malaria has a 26% better chance of surviving their birth and childhood than a baby that is homozygous for normal hemoglobin
  • 49. Figure 23.17 Distribution of malaria caused by Plasmodium falciparum (a parasitic unicellular eukaryote) Key Frequencies of the sickle-cell allele 0–2.5% 2.5–5.0% 5.0–7.5% 7.5–10.0% 10.0–12.5% >12.5%
  • 50. Why Natural Selection Cannot Fashion Perfect Organisms 1. Selection can act only on existing variations 2. Evolution is limited by historical constraints 3. Adaptations are often compromises 4. Chance, natural selection, and the environment interact © 2011 Pearson Education, Inc.

Hinweis der Redaktion

  1. Figure 23.6 One species, two populations.
  2. Figure 13.3c The Gal á pagos Islands
  3. Figure 23.2 Evidence of selection by food source.
  4. Figure 13.11a Gal á pagos finches with beaks adapted for specific diets: large ground finch
  5. Figure 23.9 Genetic drift.
  6. Figure 23.10 The bottleneck effect.
  7. Figure 23.13 Modes of selection.
  8. Figure 23.15 Sexual dimorphism and sexual selection.
  9. Figure 23.17 Mapping malaria and the sickle-cell allele.