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Hardy-Weinberg equilibrium. if p = frequency of allele A q = frequency of allele a p + q = 1, ( p + q ) 2 = 1 p 2 + 2pq + q 2 = 1 if only law of probability affects the frequency w/ which gametes combine to form new individuals. Bisexual population

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hardy weinberg equilibrium
Hardy-Weinberg equilibrium
  • if p = frequency of allele A

q = frequency of allele a

  • p + q = 1, ( p + q )2 = 1
  • p2 + 2pq + q2 = 1
  • if only law of probability affects the frequency w/ which gametes combine to form new individuals
slide2
Bisexual population
  • Large population
  • Random mating
  • No mutation
  • Migration ~ 0
  • Natural selection does not affect the locus
slide3
A population that is in Hardy-Weinberg equilibrium will experience no change in either genotype frequency or allele frequency
  • If one or more of the conditions is violated, genotype frequency and allele frequency will change
example
Example
  • If only 6% of the population displays pale eyes (recessive gene e). What is the frequency of genotype Ee in this population?

q2 = 0.06 ---> q = 0.24

p + q = 1 ---> p = 0.76

Ee = 2pq = 2(0.76)(0.24) = 0.36

genetic variation
Genetic variation
  • Cline – a measurable, gradual change over a geographical region in the average of some phenotype character
  • Ecotype – abrupt changes in the phenotype characters within a species, which often reflect abrupt changes in local environment
slide6
Geographic isolates – semi-isolated populations prevented by some extrinsic barriers from a free flow of genes
  • Genetic polymorphism – the existence within a species or population of different forms of individuals
maintenance of balanced polymorphism
Maintenance of balanced polymorphism

(vs. transitional or directional polymorphism)

  • heterosis
  • diversifying evolution
  • frequency-dependent selection
  • selective forces operating in different directions within different patches of a fine mosaic in the population
slide8
Stabilizing, directional, diversifying or disruptive evolution
  • Speciation
    • Allopatric speciation
    • Sympatric speciation
slide10
Isolation mechanism
  • Pre-zygotic: habitat, temporal, ethological, mechanical
  • Post-zygotic
    • hybrid inviability or weakness
    • hybrid sterility
    • F2 breakdown
reduction in variation
Reduction in variation
  • inbreeding, bottlenecks, founder effect, genetic drift
  • genetic drift - random shifts in allele frequencies
slide12
Effect of small populations
  • More demographic variation, inbreeding depression, genetic drift → higher risk of extinction

Minimum viable population size

  • the threshold # of individuals that will ensure the persistence of subpopulation in a viable state for a given time interval
effective population size ne
Effective population size (Ne)
  • the size of a genetically idealized population with which an actual population can be equated genetically, Ne = N , if
    • equal sex ratio
    • equal probability of mating
    • constant dispersal rate
    • progeny per family randomly distributed
slide14
unequal sex ratio

Ne = 4 Nm˙Nf / (Nm + Nf )

  • population fluctuation

1 / Ne = (1 / t )(1/N1 + 1/N2 + … + 1/Nt)

  • non-random progeny distribution

Nk

Ne = -----------------------------------------

(N/N-1)˙Vk/k˙(1+F) + (1-F)

slide15
Effect of continental drift
  • Distribution/radiation of monotremes and marsupials
extinction and its causes
Extinction and its causes
  • Natural causes: climatic changes and stochastic event
  • Human disturbance
    • habitat alteration
    • over-exploitation
    • exotic species
    • diseases and other factors