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Evolution (Ch 22–23) - Coggle Diagram
Evolution (Ch 22–23)
Chapter 23: Evolution of Populations
23.1 Genetic variation makes evolution possible
Sources of genetic variation
Mutation
Creates new alleles (ultimate source)
Sexual reproduction
Crossing over (meiosis I)
Independent assortment
Random fertilization
Variation types
Neutral variation
No fitness difference
Geographic variation
Clines (gradual change across range)
Example: body size differences by climate
Polymorphism (discrete forms)
Example: blood types (A, B, AB, O)
23.2 Hardy–Weinberg Equilibrium (test if evolving)
Conditions (must ALL be true)
No mutation
Random mating
No gene flow (no migration)
Very large population (no drift)
No natural selection
Equation + definitions
p + q = 1
p = frequency of dominant allele
q = frequency of recessive allele
p^2 + 2pq + q^2 = 1
p^2 = homozygous dominant
2pq = heterozygous
q^2 = homozygous recessive
Using H-W
If observed genotype frequencies ≠ expected
Population is evolving (one condition violated)
23.3 Mechanisms that change allele frequencies
Natural selection
Only mechanism that consistently produces adaptation
Types
Directional selection
Shifts toward one extreme
Example: larger beaks after drought
Stabilizing selection
Favors intermediate
Example: human birth weight
Disruptive selection
Favors both extremes
Example: different seed sizes favor small + large beaks
Genetic drift (chance)
Strongest in small populations
Bottleneck effect
Sudden size reduction
Example: natural disaster reduces variation
Founder effect
Small group starts new population
Example: island colonization
Gene flow (migration)
Alleles move between populations
Reduces differences between populations
Example: pollen carried to nearby population
Mutation
Rare per gene, but powerful over time
Creates new variation for selection to act on
23.4 Natural selection is the only consistent cause of adaptive evolution
Acts on phenotypes (what selection “sees”)
But evolution = allele frequency change
Environment-specific
Trait can be beneficial in one environment, harmful in another
Example: dark fur helpful in dark habitat, harmful in snow
Chapter 22: Darwinian Evolution
22.1 Darwinian Revolution
Old ideas challenged
Young Earth
Unchanging species
Darwin’s key observations
Species vary globally + locally
Example: Galápagos finches differ by island
Traits match environments
Example: camouflage in insects
Inferences
Individuals with favorable traits leave more offspring
Favorable traits accumulate over time
22.2 Natural Selection explains unity + diversity
Requirements for natural selection
Variation
Example: different beak sizes
Heritability
Traits passed via genes
Overproduction + competition
More offspring than resources allow
Differential reproductive success
“Higher fitness” traits increase in frequency
Outcomes
Adaptation (environment-specific)
Example: antibiotic resistance in bacteria
Unity of life
Common ancestry explains shared features
Diversity of life
Different environments select different traits
22.3 Evidence for Evolution
Fossil record
Transitional forms
Example: Tiktaalik (fish → tetrapod traits)
Homology (shared ancestry)
Anatomical homology
Example: vertebrate forelimbs (human, bat, whale)
Molecular homology
DNA/protein similarity
Example: cytochrome c comparisons
Vestigial structures
Reduced/modified features
Example: whale pelvis
Biogeography
Geographic patterns support common ancestry
Example: island endemics resemble nearby mainland species
Direct observation (modern evolution)
Measurable change in real time
Example: pesticide resistance
Connections: Ch 22 ↔ Ch 23
Darwin explained the pattern + logic
Descent with modification by natural selection
Population genetics explains the math + mechanisms
Allele frequencies, H-W, drift, gene flow
Same story, different zoom level
Ch 22 = big picture
Ch 23 = population + equations
Big Picture
Evolution = descent with modification
Populations evolve (not individuals)
Change in allele frequencies over generations
Key terms
Adaptation: inherited trait that increases fitness
Fitness: reproductive success in a specific environment
Natural selection: differential survival + reproduction