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Module 1: Selección natural

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XSIQ
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Biology - Variations

Variations

If a population of insects is exposed to a particular insecticide
slight physiological and biochemical differences between members of that
population appear

Those with the variations giving them resistance to the chemical will
survive, those without will die. The variants (those possessing the
favourable variations) will pass on their 'favourable' alleles to their
offspring. Over successive generations, with exposure to the same selective
pressure or agent (the insecticide), the allele giving resistance will
increase in frequency in the population. Another example commonly used to
show the effect of selection pressures is the change in proportions of dark
and light coloured moths in the industrial areas of Britain.

There is some evidence to show that the example of the peppered moth
should be analysed with a critical eye. Students wishing to further their
understanding of the issues surrounding the peppered moth example can refer
to the following websites. PLEASE NOTE: Most Internet sites have limited
life spans. The following link have been checked and were accessible at the
time of publication:

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