Week 4: Populations, Species and Evolution The Modern Synthesis by YIMO682

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									Week 4: Populations, Species
       and Evolution

   The Modern Synthesis
   Hardy-Weinberg equilibrium
• If no selection and mating is random (i.e.,
  no processes acting to change the
  distribution of genotypes), then the
  genotypes of F1 (daughter generation)
  should be the same as the genotypes of
  F0 (parent generation.
   Hardy-Weinberg equations
• 1=p+q      (p = dominant, q = recessive)

• 1 = p2 + 2pq + q2 (square both sides)

• 1 = AA + 2Aa + aa

• Genotype ratio of 1:2:1
            Figure 03.02




                           aa = 0.5 X 0.5 = 0.25
      0.5




0.5   0.5

                             Aa = 0.5 X 0.5 = 0.25
                             aA = 0.5 X 0.5 = 0.25
                                              0.50

0.5   0.5



      0.5
                           AA = 0.5 X 0.5 = 0.25
         Example: Eye color
• In a population of 100 we have 25 blue
  eyed people
• Since the allele for blue eyes is recessive
  then the blue eyed people are “aa” (q2)
• 25% or .25 are “aa”
• The frequency of the allele for blue eyes =
  the square root of .25 = .50 (50%)
• Since p + q = 1, the allele for Brown also =
  .50 (50%)
       Example 2: Eye color
• In a population of 100 we have 16 blue
  eyed people
• Since the allele for blue eyes is recessive
  then the blue eyed people are “aa” (q2)
• q2 = 16/100 or .16
• The frequency of the allele for blue eyes =
  the square root of .16 = .40
• Since p + q = 1, the frequency of the allele
  for Brown eyes is .60 (60%)
Figure 03.02
         Example 2: Eye color
• The F1 population 300 of which 27 blue eyed
  people
• Since the allele for blue eyes is recessive then
  the blue eyed people are “aa” (q2)
• q2 = 27/300 = .09
• The frequency of the allele for blue eyes = the
  square root of .09 = .30 (30%)
• Since p + q = 1, the allele for Brown = .70 (70%)
• The frequencies of the alleles for eye color in F1
  are not the same as in F0 therefore evolution is
  taking place (selection or mate choice has
  changed the distributions)
       Can Look Like Blending
• If the phenotype is result of multiple genes each
  having an additive effect.
• Example: tallness is controlled by 3 different
  genes each with 2 alleles (one for tall and one
  for short)
• If you get the tall allele in from all 3 genes then
  you get 6 tall (++++++) and you are the tallest, if
  you get all short you get 6 short (------) and you
  are the shortest.
• But if you get half of each you are in the middle
  (+-+-+-), you are also in the middle if you get ++-
  +--).
Tall    ++++++   Since all allele
                 effects are
        +++++-   additive (all get
        ++++--   expressed), the
                 you can have
        +++---   any combination
        ++----   of 3 tall and 3
                 short and have
        +-----   the same
Short            phenotype
        ------
          Hidden Variation
• Multiple gene effects mean that natural
  selection and/or mate choice is not always
  favoring or selecting against the same
  genes
• Genes can hide in the recessive state
  when phenotype is dependent on multiple
  genes (loci).
        Phenotypic Plasticity

• Soapberry bugs and mate guarding
• Frequency dependent strategy (Oklahoma
  population), trait is plastic
• In Florida sex ratios are stable and trait is
  canalized
                Other terms
• Pleiotrophy = genes effect more than one trait
• Correlated response = phenotype is dependent
  on more than one gene, therefore selection for a
  trait effects frequency of multiple genes at the
  same time
• Maladaption
• Gene drift: sampling effect, not natural selection
  or mate choice but random sampling variation
• Fixation
Speciation and Phylogeny

        Macroevolution
•Species and Speciation
•Phylogenies: Evolutionary Trees
          Biological Species
• Reproductive isolation
  – Gene flow within species
  – No gene flow between species
• Allopathic speciation: results from
  geographic/environmental isolation
  – Selection or gene drift will eventually change
    each population in different directions and
    eventually they will be incapable of
    interbreeding
• Sympatric Speciation: Niche diversification
  – Different ways of making a living in the same
    place.
  – Specialization toward different resource
    gathering strategies leads to different
    selective forces
• Sympatric Speciation: Niche diversification
  – Different ways of making a living in the same
    place.
  – Specialization toward different resource
    gathering strategies leads to different
    selective forces




                 Time
– Darwin’s finches
– Adaptive radiation

Other isolation mechanisms
– Mechanical isolation
– Temporal isolation
– Behavioral isolation

Seagulls around the World

								
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