MECHANISMS OF EVOLUTION
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Transcript of 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 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
Calculating Allelic Frequency
Phenotype frequency
Allele frequency
First generation
Second generation
White = 0 R’ = 0.25
Pink = 0.5
Red = 0.5
R = 0.75
Phenotype frequency
Allele frequency
White = 0.125
Pink = 0.25
Red = 0.625
R = 0.75
R’ = 0.25
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
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
I. POPULATION GENETICS AND EVOLUTION C. Natural Selection Acts on
Variations 3 DIFFERENT TYPES OF NATURAL
SELECTION Stabilizing Selection Directional Selection Disruptive Selection
I. POPULATION GENETICS AND EVOLUTION C. Natural Selection Acts on
Variations 1. Stabilizing Selection:
Favors the “average” individual in a populationSelection for average size spiders
Normal variation
I. POPULATION GENETICS AND EVOLUTION C. Natural Selection Acts on
Variations 2. Directional Selection:
Favors “one direction or the other direction”
Normal variation
Selection for longer beaks
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
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”
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
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”
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
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)*
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
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”
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
HOMEWORK
Due tomorrow as soon as you walk in the door.
Pg 1 1-25
Pg. 83 1-7
Pg 117 1-10