selection and speciation simple

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  • selection & speciation
    • selection
      • directional
        • phenotypes change as environmental conditions change.
          • some individuals, falling either left or right of the mean will possess a  phenotype more suited to the new conditions
      • stabilising
        • if environmental conditions remain the same then those with phenotypes closest to the mean are favoured.
          • these individuals are more likely to pass on their alleles to the next generation
            • some individuals, falling either left or right of the mean will possess a  phenotype more suited to the new conditions
          • Stabilising selection therefore tends to eliminate phenotypes at the extremes
    • Speciation
      • The evolution of new species from existing species
        • Geographical isolation
          • a physical barrier prevents two populations from breeding with one another e.g. oceans, rivers, mountain ranges.
            • Different environmental conditions on different sides of the physical barrier mean that populations begin to adapt
              • The organisms that possess the phenotypes that are favourable to a particular environment are more likely to pass on their alleles
                • as the phenotype of a population changes, this can create a new species
                  • i.e. the two original populations can no longer interbreed to produce fertile offspring

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