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
First generation
Phenotype frequency
Allele frequency
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
Pink = 0.25
R’ = 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
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 Pg. 83
1-25
Pg. 83
1-7
Pg 117
1-10