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IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
IB Biology Evolution - Earland
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IB Biology Evolution - Earland

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  • 1. Evolution IB Biology Topic 5.4
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  • 11. Analogous Structures are features of different species that are similar in function but not necessarily in structure and which do not derive from a common ancestral feature (compare to homologous structures) and which evolved in response to a similar environmental challenge. Example: Insects and birds both have wings to fly, although their wing structure is very different this is an example of an analogous structure. The fat-insulated, streamlines shapes of seals (mammals) and of penguins (birds) is another example.
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  • 13. 5.4.4 Population size and survival
    •   It should be noted that the 'struggle for survival' in this model is a consequence of over-population .
    • The struggle takes the form of individuals in the population being 'selected for ' or 'selected against ' .
    • Survivors form the new breeding population .
    • The frequency of advantageous alleles has increased.
    • The change in the heritable characteristics is by definition evolution .  
  • 14. 5.4.5 Variation in a species.
    • Individuals in a species are not all identical, but show variations in their characteristics
  • 15. 5.4.6 Sexual reproduction and variation
    • The sources of genetic variation in a populations :
      • Meiosis and the independent assortment of chromosomes creates 2 n new combinations of chromosome in the next generation n = haploid number of chromosomes
      • Random fertilisation increases the variation in the population to 2 2n again where n = haploid number of chromosomes
      • The number of different genetic variations is increased further by cross-over in meiosis by an estimated 2 3 in addition to the two above.
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