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MECHANISMS OF EVOLUTION

MECHANISMS OF EVOLUTION. CHAPTER 15.2. I. POPULATION GENETICS AND EVOLUTION. A. Populations, Not Individuals Evolve Evolution occurs as a populations genes and their frequencies change over time Gene pool: all of a populations genes

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MECHANISMS OF EVOLUTION

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  1. MECHANISMS OF EVOLUTION CHAPTER 15.2

  2. I. POPULATION GENETICS AND EVOLUTION • A. Populations, Not Individuals Evolve • Evolution occurs as a populations genes and their frequencies change over time • Gene pool: all of a populations genes • Allelic frequency: the percentage of any specific allele in a gene pool • Genetic equilibrium: when the frequency of a populations allele remains the same over time

  3. Calculating Allelic Frequency Phenotype frequency Allele frequency First generation White = 0 R’ = 0.25 Pink = 0.5 R = 0.75 Red = 0.5 Second generation Phenotype frequency Allele frequency White = 0.125 R = 0.75 R’ = 0.25 Pink = 0.25 Red = 0.625

  4. I. POPULATION GENETICS AND EVOLUTION • B. Changes in Genetic Equilibrium • Population in G.E. is NOT evolving • You must disrupt G.E. for a population to evolve • Things that can disrupt G.E. • Mutations • Environmental factors • Chemicals or radiation exposure • Genetic drift: the alteration of allelic frequencies by chance events

  5. I. POPULATION GENETICS AND EVOLUTION • B. Changes in Genetic Equilibrium • Genetic equilibrium also disrupted by immigration and emigration • Which is “into”? Which is “out of”? • Gene flow: the transport of genes by migrating individuals

  6. I. POPULATION GENETICS AND EVOLUTION • C. Natural Selection Acts on Variations • 3 DIFFERENT TYPES OF NATURAL SELECTION • Stabilizing Selection • Directional Selection • Disruptive Selection

  7. I. POPULATION GENETICS AND EVOLUTION • C. Natural Selection Acts on Variations • 1. Stabilizing Selection: • Favors the “average” individual in a population Normal variation Selection for average size spiders

  8. I. POPULATION GENETICS AND EVOLUTION • C. Natural Selection Acts on Variations • 2. Directional Selection: • Favors “one direction or the other direction” Selection for longer beaks Normal variation

  9. I. POPULATION GENETICS AND EVOLUTION • C. Natural Selection Acts on Variations • 3. Disruptive Selection: • Favors “both directions” Selection for light limpets Normal variation Selection for dark limpets

  10. I. POPULATION GENETICS AND EVOLUTION • C. Natural Selection Acts on Variations • All of these types of natural selection will favor one specific trait in a species • This selection can lead to the “evolution of a new species”

  11. II. THE EVOLUTION OF SPECIES • Speciation: the evolution of a new species • Occurs when members of a similar population can no longer interbreed and produce fertile offspring • A. Physical Barriers that Can Prevent Interbreeding • Geographic isolation: occurs whenever a physical barrier separates a species • Can be a land barrier or an ocean barrier • New species evolve when G.I. occurs

  12. II. THE EVOLUTION OF SPECIES • B. Reproductive Isolation can Result in Speciation • Reproductive isolation: occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring (P.F.O.) • C. A Change in Chromosome Numbers and Speciation • Polyploid: any individual or species with a multiple of the normal set of chromosomes • Results from an error in “meiosis”

  13. II. THE EVOLUTION OF SPECIES • D. Speciation Rates • Gradualism: is the idea that species originate through a “gradual” change over time. • Punctuated equilibrium: argues that speciation occurs relatively quickly, in rapid bursts, with long periods of genetic equilibrium in between. • due to: environmental changes and introduction of new species into an environment

  14. III. PATTERNS OF EVOLUTION • A. Diversity in New Environments • 2 types of evolution associated with being moved to a new environment • Adaptive radiation • Divergent evolution • 1. Adaptive Radiation: • When ancestral species evolve into an array of species to fit a number of diverse habitats • Darwin’s study on “finches” *(a type of bird; he compared the shapes of their beaks)*

  15. III. PATTERNS OF EVOLUTION • A. Diversity in New Environments • 2. Divergent Evolution: • Is s type of “adaptive radiation” • Is a pattern of evolution in which similar species diverge and become increasingly distinct/different. • Occurs when a population changes as they adapt to different environments

  16. III. PATTERNS OF EVOLUTION • B. Different Species can Look Alike • Convergent evolution: a pattern of evolution where distantly related organisms evolve similar traits/characteristics • Occurs when unrelated species occupy similar environments • Polar bear and a “Snowy Owl” or “White Fox”

  17. TODAYS ASSIGNMENT • Pg. 133 #1-4 • Pg. 137 #1-4 • Pg. 142 #1-4 • Pg. 146 #1-3 • Pg. 147 #1-6 • Should be a total of 21 questions • Turn in to me before you leave

  18. HOMEWORK • Due tomorrow as soon as you walk in the door. • Pg 1 • 1-25 • Pg. 83 • 1-7 • Pg 117 • 1-10

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