Natural Selection

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  • Created by: Holly
  • Created on: 13-02-14 17:54
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  • Natural Selection
    • Examples
      • Orchids
        • Pyramidal orchids produce a scent to attract male moths
        • Some look like female wasps to attract a particular species of male wasp
      • Woodpeckers
        • Lesser spotted woodpecker prefers to feed from finer branches at the tops of trees
        • Great spotted woodpecker prefers to feed from the broader branches
        • Green woodpecker prefers to feed from the ground
      • Headlice
        • They have become resistant to the insecticides in shampoos
        • insecticide-resistant alleles in head lice have gone from being quite rare in pre-insecticide populations to extremely common
    • Survival of the fittest
      • Some individuals by chance have a characteristic that gives them an advantage over others
      • 'fit' = well adapted
    • Evolution
      • A change in allele frequency in a population over time
      • For natural selection to lead to evolution there must be some genetic variation
      • An allele may have no obvious advantage or disadvantage but it may become selectively advantageous if the environment changes
    • Process of evolution
      • 1. A population has some naturally-occuring genetic variation with new alleles created through mutations.
        • 2. A change in the environment causes a change in the selection pressures acting on the population
          • 3. An allele which was previously of no particular advantage now becomes favourable
            • 4. Organisms with the allele are more likely to survive, reproduce and so produce offspring
              • 5. Their offspring are more likely to have the allele so it becomes more common in the population


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