IB Biology Evolution - Earland
Transcript of IB Biology Evolution - Earland
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EvolutionIB Biology Topic 5.4
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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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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.
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5.4.5 Variation in a species.
• Individuals in a species are not all identical, but show variations in their characteristics
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5.4.6 Sexual reproduction and variation
• The sources of genetic variation in a populations :▫Meiosis and the independent assortment of
chromosomes creates 2n new combinations of chromosome in the next generation n = haploid number of chromosomes
▫Random fertilisation increases the variation in the population to 22n again where n = haploid number of chromosomes
▫The number of different genetic variations is increased further by cross-over in meiosis by an estimated 23 in addition to the two above.
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