Gene Pools, Selection

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Gene Pools, Selection Drift
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Terms

• Population localized group of individuals
  belonging to the same species
• Species group of pops. whose individuals have
  the potential to interbreed and produce fertile
  offspring
• Gene Pool total aggregate of genes in a pop at
  any one time
• Speciation the formation of new species

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Natural Variation in Phenotype

• Each kind of gene in gene pool may have two or
  more alleles
• Individuals inherit different allele combinations
• This leads to variation in phenotype
• Offspring inherit genes, not phenotypes

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What determines the allele combos in a Gene Pool

• 1. Gene mutation
• 2. Change in chromo or structure
• 3. Crossing over at meiosis I
• 4. Independent assortment at meiosis I
• 5. Fertilization
• ONLY MUTATIONS CREATE NEW ALLELES!

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Genetic Equilibrium

• Allele frequencies at a locus are not changing
• Population is not evolving

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Hardy-Weinberg Rule

• At genetic equilibrium, proportions of genotypes
  at a locus with two alleles are given by the
  equation
• p2 (AA) 2pq (Aa) q2 (aa) 1
• Frequency of allele A p
• Frequency of allele a q

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Punnett Square
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Frequencies in Gametes
F1 genotypes
Gametes
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Five Conditions

• 1. No mutation
• 2. Random mating
• 3. Gene doesnt affect survival or reproduction
• 4. Large population
• 5. No immigration/emigration

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Gene Flow

• Physical flow of alleles into a population
• Tends to keep the gene pools of populations
  similar
• Counters the differences that result from
  mutation, natural selection, and genetic drift
• Balanced polymorphism (variation)

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Balanced Polymorphism

• Polymorphism - having many forms
• Occurs when two or more alleles are maintained at
  frequencies greater than 1 percent
• Variation is good lotto!

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No Change through Generations
STARTING POPULATION
490 AA butterflies Dark-blue wings
420 Aa butterflies Medium-blue wings
90 aa butterflies White wings
THE NEXT GENERATION
490 AA butterflies
420 Aa butterflies
90 aa butterflies
NO CHANGE
THE NEXT GENERATION
490 AA butterflies
420 Aa butterflies
90 aa butterflies
NO CHANGE
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Microevolutionary Processes

• Drive a population away from genetic equilibrium
• Small-scale changes in allele frequencies brought
  about by
• Natural selection
• Gene flow
• Genetic drift
• Inbreeding
• Artificial Selection

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Gene Mutations

• Increase gene pool variation raw material for
  evolution
• Infrequent but inevitable
• Each gene has own mutation rate
• Lethal mutations
• Neutral mutations
• Advantageous mutations

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Natural Selection

• A difference in the survival and reproductive
  success of different phenotypes
• Acts directly on phenotypes and indirectly on
  genotypes

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Reproductive Capacity Competition

• All populations have the capacity to increase in
  numbers
• No population can increase indefinitely
• Eventually the individuals of a population will
  end up competing for resources

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Directional Selection
Number of individuals in the population
Range of values for the trait at time 1

• Allele frequencies shift in one direction
• Ex Pesticide resistance, Antibiotic resistance,
  peppered moth

Number of individuals in the population
Range of values for the trait at time 2
Number of individuals in the population
Range of values for the trait at time 3
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Stabilizing Selection
Number of individuals in the population

• Intermediate forms are favored and extremes are
  eliminated
• Ex Gall-making fly has two major predators
• Wasps prey on larvae in small galls
• Birds eat larvae in large galls
• Flies that cause intermediate-sized galls have
  the highest fitness

Range of values for the trait at time 1
Range of values for the trait at time 2
Range of values for the trait at time 3
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Disruptive Selection
Number of individuals in the population

• Forms at both ends of the range of variation are
  favored
• Intermediate forms are selected against
• Ex Selection favors birds with very large or
  very small bills
• Birds with intermediate-sized bill are less
  effective feeders

Range of values for the trait at time 1
Number of individuals in the population
Range of values for the trait at time 2
Number of individuals in the population
Range of values for the trait at time 3
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Sexual Selection

• Selection favors certain secondary sexual
  characteristics
• Through nonrandom mating, alleles for preferred
  traits increase
• Leads to increased sexual dimorphism

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Sexual Selection

• Traits which attract mates
• Include behavioral, structural and physiological
• May work against natural selection or have no
  affect.
• Fitness - it is the one who passes on its genes
  (mates effectively) which will create future
  generations!

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Peacock
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Cuttlefish mating spermatophorelike a phone
number
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Guppies

• Drab Females vs. Colorful males!

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Genetic Drift

• Random change in allele frequencies brought about
  by chance not selection
• Effect is most pronounced in small populations
• Sampling error - Fewer times an event occurs,
  greater the variance in outcome
• Founder Effect
• Inbreeding

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Bottleneck

• A severe reduction in population size
• Causes pronounced drift, alleles are lost

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Founder Effect

• Effect of drift when a small number of
  individuals starts a new population
• By chance, allele frequencies of founders may not
  be same as those in original population
• Effect is pronounced on isolated islands/areas
• Polydactylism in Amish

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Inbreeding

• Nonrandom mating between related individuals
• Leads to increased homozygosity
• Can lower fitness when deleterious recessive
  alleles are expressed

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Artificial Selection

• Traits NOT selected for by nature, but by man
• AKA selective breeding
• Domestication of animals dogs, cats, etc
• Bred for behavioral and physical traits NOT
  necessarily best fit for organisms natural
  environment
• Humans can CAUSE evolution do it every day
  soaps, pet breeds, weed killer, food
  industry/agriculture.
• THE EVOLUTION EXPLOSION

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Canus familiaris lots of variation selected for
by humans!