Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884)...
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Transcript of Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884)...
![Page 1: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/1.jpg)
Chapter 23
The Evolution of Populations
![Page 2: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/2.jpg)
Western Historical Context
Gregor Mendel (1822-1884)
Austrian monk whose breeding experiments with peas shed light on the rules of inheritance
Mendel was a contem-porary of Darwin, but his work wasoverlooked until the 20th century
![Page 3: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/3.jpg)
Western Historical Context
A conceptual synthesis of Darwinian evolution, Mendelian inheritance, and modern population genetics
The Modern Synthesis (early 1940s)
![Page 4: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/4.jpg)
Potential for rapid population growth when resources
are not limiting
Resource availability generally limits population size
Competition for resources(“struggle for existence”)
Phenotypic variability (morphology, physiology,
behavior, etc.)
Natural Selection: Survival and reproduction
of the “fittest” individuals
Some variabilityresults from heritable genotypic differences
![Page 5: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/5.jpg)
Phenotype vs. Genotype
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Phenotype vs. Genotype
Phenotype: all expressed traits of an organism
![Page 7: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/7.jpg)
Phenotype vs. Genotype
Phenotype: all expressed traits of an organism
Genotype: the entire genetic makeup of an individual (i.e., its genome – it’s full complement of genes and the two alleles that comprise each locus), or a subset of an individual’s genes
![Page 8: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/8.jpg)
Evolution
A change in allele frequency in a population (a change in the
gene pool)
Population = all of the individuals of a species in a given area
![Page 9: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/9.jpg)
Potential for rapid population growth when resources
are not limiting
Resource availability generally limits population size
Competition for resources(“struggle for existence”)
Phenotypic variability (morphology, physiology,
behavior, etc.)
Natural Selection: Survival and reproduction of the
“fittest” individuals
Some variabilityresults from heritable genotypic differences
Adaptive evolution: A change in the phenotypic constitution of a population owing to selection on heritable variation
among phenotypes that changes the genotypic constitution of the population
![Page 10: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/10.jpg)
Population Genetics
Examines the frequency, distribution, and inheritance of
alleles within a population
![Page 11: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/11.jpg)
Hardy-Weinberg Equilibrium
The population genetics theorem that states that the frequencies of
alleles and genotypes in a population will remain constant
unless acted upon by non-Mendelian processes (i.e., mechanisms of
evolution)
![Page 12: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/12.jpg)
See Figs. 23.4 & 23.5 – An example
![Page 13: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/13.jpg)
See Figs. 23.4 & 23.5 – An example
![Page 14: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/14.jpg)
See Figs. 23.4 & 23.5 – An example
![Page 15: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/15.jpg)
This means that 80% of sperm & eggs will carry R, and 20% of sperm & eggs will carry r
See Figs. 23.4 & 23.5 – An example
![Page 16: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/16.jpg)
Under strict Mendelian inheritance, allele frequencies would remain constant from one generation to the next
(Hardy-Weinberg Equilibrium)
Allele Frequencies
RRp2=0.64
Rrpq=0.16
rRqp=0.16
rrq2=0.04
RSperm Eggs
Genotype frequencies: p2=0.64 (RR) 2pq=0.32 (Rr) q2=0.04 (rr)
Allele frequencies: p=0.8 (R) q=0.2 (r)
R
rr
80% (p=0.8)80% (p=0.8)
20% (q=0.2)20% (q=0.2)
![Page 17: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/17.jpg)
At a later date, you determine the genotypes of 500 individuals, and find the following:
Allele Frequencies
280 RR
165 Rr
55 rr
Frequency of R (a.k.a. “p”): 280 + 280 + 165 = 725 R alleles in the pop. 725 / 1000 = 0.725
Frequency of r (a.k.a. “q”): 165 + 55 + 55 = 275 r alleles in the pop. 275 / 1000 = 0.275
![Page 18: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/18.jpg)
The frequencies of alleles R and r have changed:
Allele Frequencies
320 RR160 Rr 20 rr
T1:
p=0.8, q=0.2
280 RR165 Rr 55 rr
T2:
p=0.725, q=0.275
The population has
EVOLVED!
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For a two-allele locus: Let p = the frequency of one allele in the population (usually the dominant) Let q = the frequency of the other allele
Hardy-Weinberg Equation
p2 + 2pq + q2 = 1
Notice that: p + q = 1 p = 1 – q q = 1 – p
Genotypes should occur in the population according to:
![Page 20: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/20.jpg)
Hardy-Weinberg Equation
p2 + 2pq + q2 = 1
p2 = proportion of population that is homozygous for the first allele
(e.g., RR)
2pq = proportion of population that is heterozygous (e.g., Rr)
q2 = proportion of population that is homozygous for the second
allele (e.g., rr)
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Hardy-Weinberg Equation
p2 + 2pq + q2 = 1
Given either p or q, one can solve for the rest of the above equation
What would q be if p = 0.6?
What would 2pq be if p = 0.5?
![Page 22: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/22.jpg)
Hardy-Weinberg Equation
p2 + 2pq + q2 = 1
Given the frequency of either homozygous genotype, the rest of the equation can be solved
What would q be if p2 = 0.49?
Hint: q = q2
![Page 23: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/23.jpg)
Hardy-Weinberg Equilibrium
Is a null model…
like Newton’s first law of motion:
Every object tends to remain in a stateof uniform motion (or stasis), assuming no external
force is applied to it
The Hardy-Weinberg Equation will be satisfied, as long as all the assumptions are met…
![Page 24: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/24.jpg)
Hardy-Weinberg Equilibrium
Assumptions:
1) Infinite population size
Because genetic drift affects smaller populations more than larger pops.
Genetic drift = allele frequency change due to chance
Genetic drift reduces genetic variability
![Page 25: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/25.jpg)
See Fig. 23.7 Genetic drift in a small population of wildflowers
![Page 26: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/26.jpg)
See Fig. 23.7 Genetic drift in a small population of wildflowers
![Page 27: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/27.jpg)
See Fig. 23.7 Genetic drift in a small population of wildflowers
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Genetic drift often results from populations passing through a population bottleneck
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Genetic drift often results from populations passing through a population bottleneck
![Page 30: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/30.jpg)
The founder effect is an example of a population bottle neck
Mainlandpopulation
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Mainlandpopulation
Colonists from themainland colonize
an island
The founder effect is an example of a population bottle neck
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Mainlandpopulation
Colonists from themainland colonize
an island
Island gene poolis not as variable
as the mainland’s
The founder effect is an example of a population bottle neck
![Page 33: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/33.jpg)
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Hardy-Weinberg Equilibrium
Assumptions:
1) Infinite population size (no genetic drift) 2) No gene flow among populations
Gene flow = transfer of alleles among populations
Emigration transfers alleles out of a population and immigration transfers them in
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Gene flow connects populations
Populationat t1
Island gene poolis not as variable
as the mainland’s
Population at t2
(after immigration)
time
![Page 36: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/36.jpg)
Gene flow connects populations
Populationat t1
Island gene poolis not as variable
as the mainland’s
![Page 37: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/37.jpg)
Gene flow connects populations
Populationat t1
Island gene poolis not as variable
as the mainland’s
Population at t2
(after immigration)
time
![Page 38: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/38.jpg)
Hardy-Weinberg Equilibrium
Assumptions:
1) Infinite population size (no genetic drift) 2) No gene flow among populations 3) No mutations
![Page 39: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/39.jpg)
Populationat t1
Island gene poolis not as variable
as the mainland’s
Population at t2
(after immigration)
time
Mutations generally boost genetic diversity
![Page 40: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/40.jpg)
Populationat t1
Island gene poolis not as variable
as the mainland’s
Population at t2
(after a mutation event)
time
Mutations generally boost genetic diversity
![Page 41: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/41.jpg)
Hardy-Weinberg Equilibrium
Assumptions:
1) Infinite population size (no genetic drift) 2) No gene flow among populations 3) No mutations4) Random mating with respect to genotypes
E.g., imagine what would happen if RR males mated only with rr females
Those particular matings would result in no RR or rr offspring, thereby altering population-wide genotype frequencies
![Page 42: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/42.jpg)
Hardy-Weinberg Equilibrium
Assumptions:
1) Infinite population size (no genetic drift) 2) No gene flow among populations 3) No mutations 4) Random mating with respect to genotypes 5) No natural selection
E.g., imagine what would happen if rr flowers were the only ones that ever attracted pollinators (even though the population contains RR and Rr individuals as well)
![Page 43: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/43.jpg)
Hardy-Weinberg Equilibrium
Assumptions:
1) Infinite population size (no genetic drift) 2) No gene flow among populations 3) No mutations4) Random mating with respect to genotypes5) No natural selection
![Page 44: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/44.jpg)
Adaptive evolution: A change in the phenotypic constitution of a population owing to selection on heritable variation
among phenotypes that changes the genotypic constitution of the population
Variation within Populations
Let’s briefly review…
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Variation within Populations
Since selection acts on phenotypes, yet evolution requires population-level genotypic
change, it is important to understand intraspecific variation
Note: If all individuals were phenotypically identical, there would be no opportunity for
selection
Note: If all individuals were genotypically identical, there would be no opportunity for
evolution
![Page 46: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/46.jpg)
Variation within Populations
Phenotypic variation results from both environmental and genetic influences
Consider identical vs. fraternal twins
![Page 47: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/47.jpg)
Variation within Populations
Phenotypic variation results from both environmental and genetic influences
Phenotypic variation within populations is either discrete or quantitative/continuous
Discrete variation: polymorphism = mutiple phenotypes that are readily
placed in distinct categories co-occur
(e.g., our red and white flowers result from a polymorphic locus)
E.g., a “bar graph” trait like ABO blood type
![Page 48: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/48.jpg)
Variation within Populations
Phenotypic variation results from both environmental and genetic influences
Phenotypic variation within populations is either discrete or quantitative/continuous
Continuous variation: quantitative characters = multiple loci produce a trait (e.g., flower size), and the trait varies
continuously in the population
E.g., a “bell curve” trait like human height
![Page 49: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/49.jpg)
Variation within Populations
Phenotypic variation results from both environmental and genetic influences
Phenotypic variation within populations is either discrete or quantitative/continuous
Phenotypic variation also exists among populations
E.g., geographic variation
Heliconius species A
Heliconius species B
![Page 50: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/50.jpg)
How is genetic variation maintained?
Variation within Populations
1) Diploidy provides heterozygote protection
2) Balanced polymorphism Heterozygote advantage
E.g., A locus for one chain of hemoglobin in humans has a recessive allele that causes sickle-cell anemia in homozygotes, but provides resistance to malaria in heterozygotes
![Page 51: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/51.jpg)
How is genetic variation maintained?
Variation within Populations
1) Diploidy provides heterozygote protection
2) Balanced polymorphism Heterozygote advantageFrequency-dependent selection
3) Neutrality
![Page 52: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/52.jpg)
Fitness
Darwinian fitness = an individual’s reproductive success (genetic contribution to subsequent generations)
Relative fitness = a genotype’s contribution to subsequent generations compared to the contributions of alternative genotypes at the same locus
![Page 53: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/53.jpg)
Effects of Selection
See Fig. 23.12
Coat color
![Page 54: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/54.jpg)
Directional selection consistently favors phenotypes at one extreme
Effects of Selection
See Fig. 23.12
Coat color
Coat color
![Page 55: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/55.jpg)
Stabilizing selection favorsintermediate phenotypes
Effects of Selection
See Fig. 23.12
Coat color
Coat color
![Page 56: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/56.jpg)
Diversifying (disruptive) selection simultaneously favors both phenotypic extremes
Effects of Selection
See Fig. 23.12
Coat color
Coat color
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Effects of Selection
Directional, diversifying (disruptive), and stabilizing selection
See Fig. 23.12
Coat color
Coat color Coat color Coat color
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Sexual Selection
Intrasexual selection, usually male-male competition
![Page 59: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/59.jpg)
Sexual Selection
Dynastes tityus
Often leads to sexual dimorphism & exaggerated traits
Intrasexual selection, usually male-male competition
![Page 60: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/60.jpg)
Sexual Selection
Dynastes hercules
Intrasexual selection, usually male-male competition
Often leads to sexual dimorphism & exaggerated traits
![Page 61: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/61.jpg)
Sexual Selection
Lucanus elaphus
Intrasexual selection, usually male-male competition
Often leads to sexual dimorphism & exaggerated traits
![Page 62: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/62.jpg)
Sexual Selection
Intersexual selection, usually female mate choice
![Page 63: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/63.jpg)
Sexual Selection
Intersexual selection, usually female mate choice
Often leads to sexual dimorphism & exaggerated traits
![Page 64: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/64.jpg)
Sexual Selection
Intersexual selection, usually female mate choice
Often leads to sexual dimorphism & exaggerated traits
![Page 65: Chapter 23 The Evolution of Populations. Western Historical Context Gregor Mendel (1822-1884) Austrian monk whose breeding experiments with peas shed.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649ce25503460f949ae481/html5/thumbnails/65.jpg)
Sexual Selection
Intersexual selection, usually female mate choice
Often leads to sexual dimorphism & exaggerated traits