Mead AP Biology
LAP 6 Population Genetics and Evolution
Chapters 22-24
22.1 Challenge to Traditional Views: Historical Context for Darwin
A. Resistance to Idea of Evolution
◦ Scale of Nature
 Plato
 Aristotle
◦ Judeo-Christian Natural Theology
 Linnaeus
◦ Catastrophism
 Cuvier studies fossils
 Paris basin
 Extinction NOT due to evolution
B. Gradualism
◦ Hutton
◦ Lyell- Uniformitarianism
◦ Fig. 22.2 Timeline
C. Lamarck
◦ Use and Disuse theory, 1809
◦ Inheritance of acquired characteristics
◦ Some good points
◦ Mechanism not correct
22.2 Darwinian Revolution
A. Darwin’s Research
◦ Voyage of HMS Beagle 1831
 Fig 22.5
◦ Focus on Adaptation
 Return 1836
 Connect adaptation to origin of new species
 Geographical barriers lead to divergence
 Finches, Fig 22.6
◦ Alfred Russel Wallace
 Same ideas as Darwin
 Sent to Darwin for review in 1858
 Presented by Lyell and Wallace
 Darwin published later in 1859
B. Origin of Species
◦ Descent with Modification, Fig 22.7
 Occurrence of evolution
 Unity of life
 Common Ancestor
◦ Natural Selection and Adaptation
 Mechanism of evolution
 3 key components
1. Differential reproductive success
 Malthus Doctrine of Human Suffering
 Over-reproduction
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 Struggle for existence based on limited resources
2. Interaction of environment and existing variability
3. Product is adaptation to environment
Evidence from artificial selection
 Fig 22.10 Wild mustard  Cabbage
 Dramatic results in short time
 Natural selection should be able to do in hundreds or thousands of generations
Points to remember
 Individuals don’t evolve, populations evolve
 Can only amplify or diminish heritable variations that already exist
 Traits favored by natural selection are situational
 Vary by time or place
22. 3 Darwin’s Theory Explains Wide Range of Observations
A. Natural Selection in Action
◦ Differential predation and guppy population
 Fig 22.12
◦ Evolution of drug-resistant HIV
 Fig 22.13
B. Homology
◦ Def
◦ Anatomical homology
 Homologous structures, Fig 22.14
 Comparative embryology, Fig 22.15
 Vestigial structures
◦ Molecular Homology, Fig 22.16
C. Biogeography
◦ Def
◦ Fig 22.17
D. Fossil Record
◦ Transitional forms
◦ Fig 22.18
23.1 Population Genetics
A. Modern Synthesis
◦ Joining of Darwin and Mendel’s work
◦ Population genetics
◦ Gradualism
◦ Modern synthesis
B. Genetic Structure of Populations
◦ Population
 Def
 Geographic range, Fig 23.3
◦ Gene pool
 Def
 Fixed allele
◦ Allele frequencies
 p and q

Example: 500 plants
 320 red, 160 pink, 20 white
C. Hardy-Weinberg Theory: Non-evolving Populations
◦ Frequencies remain constant
◦ p + q = 1 (100%) Allele frequencies
◦ Homozygous dominant = p2
◦ Heterozygous = pq + pq = 2pq
◦ Homozygous recessive = q2
◦ Hardy-Weinberg Equation
 p2 + 2pq + q2 = 1 (100%)
 Genotype frequencies
◦ Use to calculate frequencies for alleles or genotypes for a gene pool
◦ Fig 23.5
◦ Solving problems: 1 in 10,000 suffer from PKU which is a recessively inherited
disorder. What is the allele frequency for the dominant and recessive allele? What
is the frequency for carriers? Assume Hardy-Weinberg equilibrium.
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Conditions for Hardy-Weinberg Equilibrium
 Very large population
 Smaller populations subject to genetic drift
 No gene flow
 No movement of genes in or out of gene pool
 No new mutations
 No modifications to gene pool
 Random mating
 No choosing of mates based on any phenotype
 No natural selection
 No differential survival based on traits
More sample problems:
If the frequency for the A allele is 70%, what is the frequency of individuals that
are heterozygous?
If 16% of individuals are homozygous recessive for a trait what is the frquency of
the dominant allele?
23.2 Mutation and Sexual Recombination Produce Variation
A. Mutation
◦ In cell lines that produce gametes
◦ Point mutations: small vs large effect
 Alter protein function
◦ Chromosome mutations
◦ Effect depends on generation length
B. Sexual recombination
◦ Occur every generation
◦ Most variation due to this
23.3 Altering Population’s Genetic Composition
A. Deviations from Hardy-Weinberg
◦ Any can cause evolution
◦ Mutation effects are small
◦ Recombination shuffles but doesn’t change frequencies
◦ Nonrandom mating
 Changes genotype frequencies
 Doesn’t affect allele frequencies
◦ Other 3 are major causes of evolution
B. Genetic Drift
◦ Def
◦ Fig 23.7
◦ 2 types
 Bottleneck effect, Fig 23.8
 Founder effect
C. Gene Flow
◦ Def
◦ Reduces differences between populations
23.4 Natural Selection: Primary mechanism for adaptive evolution
A. Genetic variation
1. Variation within population
 Discrete characters
 Quantitative characters
 Polymorphism
 Measuring genetic variation
 Average heterozygosity
2. Variation between populations
 Geographical variation
 Due to natural selection or genetic drift
 Cline
 Fig 23.11: Inquiry example
B. Natural Selection: Closer look
◦ Evolutionary fitness
◦ Modes of selection, Fig 23.12
1. Directional selection
2. Stabilizing selection
3. Disruptive selection
C. Preserving Variation
◦ Diploidy
◦ Balancing Selection
 Balanced Polymorphism
 Def
 Due to 3 causes
1. Heterozygote advantage
2. Patchy environment
3. Frequency dependent selection
◦ Neutral Variation
D. Sexual selection
◦ Def
◦ Leads to sexual dimorphism
 Fig 23. 15
◦ Intrasexual selection
◦ Intersexual selection
E. Natural selection doesn’t make perfect organism
◦ Limited by historical constraints
◦ Adaptations are often compromises
◦ Chance and selection interact
◦ Selection only acts on variations that exist
◦ Operates on a “better than” basis
24.1 What is a Species?
A. Biological Species Concept
◦ Def
◦ Occur in natural environment
B. Reproductive Isolation
◦ Biological barriers
◦ Summarized in Fig 24.4
◦ Pre-zygotic barriers
 Impede mating
1. Habitat isolation
2. Behavioral isolation
3. Temporal isolation
 Impede fertilization
1. Mechanical isolation
2. Gametic isolation
◦ Post-zygotic barriers
 Def
 Reduced hybrid viability
 Reduced hybrid fertility
 Hybrid breakdown
C. Limitations to biological species concept
D. Other definitions of species
◦ Morphological species concept
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Paleontological species concept
Ecological species concept
Phylogenic species concept
24.2 Modes of Speciation
A. Allopatric speciation
◦ Geographical barriers
◦ Fig 24.6 Example
◦ Conditions favoring allopatric speciation
 Small populations
 Fringe isolation: Splinter population or peripheral isolate
 Why good candidates
B. Sympatric speciation
◦ Def
◦ Genetic change creates reproductive barrier
◦ Polyploidy in plants
 Def
 Fig 24. 8 Autoploidy
◦ Alloploidy
 Def
 More common form of polyploidy
 Hybrid usually sterile but can use asexual repro.
 Mutation may allow sex repro
 Fig 24.9
◦ Animal sympatric speciation
 Polyploidy less common than in plants
 Utilize other mechanisms
 Reproductive isolation
 Differences in resource utilization
 Habitat differentiation
 Sexual selection
 Cichlids, Fig 24.10
C. Adaptive Radiation
◦ Def
◦ Example: Hawaii
 Fig 24.12
D. Tempo of Speciation
◦ Punctuated equilibrium
◦ Def, Fig 24.13
◦ Fossil record
◦ Relative speed
◦ Debate
◦ Gradualism
24.3 Macroevolution is Combo of Many Speciation Events
A. Evolutionary Novelties
◦ Improved versions of simpler structures
◦ Fig 24.14
B. Evolution of Genes that Control Dev’t
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Changes in rate and timing
 Heterochrony
 Allometric growth
 Fig 24.15
 Fig 24. 16 Salamanders Heterochrony
 Fig 24. 17 Paedomorphosis
 Def
Changes in spatial pattern
 Homeotic genes
 Hox genes
 Fig 24.18 and 24.19
Evolution is NOT goal oriented!