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Population Genetics. Hardy-Weinberg and More. Variation of Traits in a Population. Bell Curve Extremes at each end Causes of Variation Environment and heredity Mutation Recombination Random fusion of gametes. Allele frequencies and Gene Pool.

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population genetics

Population Genetics

Hardy-Weinberg and More

variation of traits in a population
Variation of Traits in a Population
  • Bell Curve
    • Extremes at each end
  • Causes of Variation
    • Environment and heredity
    • Mutation
    • Recombination
    • Random fusion of gametes
allele frequencies and gene pool
Allele frequencies and Gene Pool
  • Total genetic information available in population
  • Allele frequency is determined by dividing number of certain allele by total number of alleles.
    • P + Q = 1
      • P = number of recessive/total number of alleles
      • Q =number of dominant/total number of alleles
  • Predicting Phenotypes
    • Phenotype frequency
      • Equal to the number of individuals with particular phenotype divided by the total number of individuals in the population.
      • Same principle as allele frequencies
      • P2 + 2PQ + Q2 = 1
hardy weinberg equilibrium
Hardy Weinberg Equilibrium
  • Allele frequencies in a population remain the same from generation to generation unless acted on by outside influences.
  • Assumptions about an ideal “made up” population that is not evolving
    • No net mutations occur
    • Individuals neither enter nor leave the population.
    • The population is large
    • Individuals mate randomly.
    • Natural Selection does not occur.
what is microevolution1
What is Microevolution?
  • A change in the gene frequency of a population
  • Can be seen over short periods of time
    • One generation to the next
    • For example, the frequency of a gene for pesticide resistance in a population of crop pests increases
    • There can be many reasons for microevolution
disruption of genetic equilibrium
Disruption of Genetic Equilibrium
  • Mutation
    • Can produce totally new alleles for a trait
    • Most are harmful but the beneficial ones are important for evolution
  • Migration
    • Immigration: Movement of individuals into a population
    • Emigration: Movement of individuals out a population
      • This is gene flow, the process of genes moving from one population to another
disruption of genetic equilibrium1
Disruption of Genetic Equilibrium
  • Genetic Drift
    • Allele frequencies change as a result of random events or chance
    • Small populations
      • a) Founders effect
      • b) Bottle neck
  • Non-Random Mating
    • Many species do not mate randomly
    • Based on geographic proximity and similar physical characteristic
disruption of genetic equilibrium3
Disruption of Genetic Equilibrium
  • Natural Selection
    • Stabilizing selection
      • Individuals with average form of trait have highest fitness
      • Extreme forms have lower fitness
    • Directional selection
      • One extreme form has greater fitness then average
    • Disruptive Selection
      • Either extreme have greater fitness
disruption of genetic equilibrium4
Disruption of Genetic Equilibrium
  • Sexual Selection
    • Colors
    • Females choose males based on certain traits
    • Extreme traits give female indication of quality of males genes