Variation & Evolution

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  • Variation & Evolution
    • Population Genetics
      • Allele frequency = Frequency of alleles within a genepool
      • Gene pool remains stable if the environment remains stable
      • If the environment changes some phenotypes will have a selective advantage
        • Some will have a selective disadvantage.
          • The frequency of these alleles will decrease
        • This will cause a change in allele frequency
        • The frequency of these alleles will increase
      • Selection pressures have an effect on the frequency of alleles
      • Open population = overlapping populations (immigration of alleles)
        • Closed population = barriers between populations
    • Why would a gene pool change?
      • Mutation
      • Genetic Drift
        • A random change in the frequency of an allele in a population/ gene pool
        • The alleles in the offspring are a sample of those in the parents
        • There is an element of chance in determining whether any given individual survives and reproduces
        • Can cause alleles to completely disappear from a population and therefore reduces genetic variation
        • E.G Darwin's Finches
          • They were geographically isolated on different islands and had to adapt to the food supplies and the new environment
          • Formed from a common ancestor
            • Adaptive Radiation
      • Disasters that result in the loss of a section of a population
      • Natural selection - loss of genes because individuals are unable to compete / survive and breed


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