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Asya.C asked in 科學動物學 · 1 decade ago


1.Describe a gene pool and the factors that affect it.

2.differentiate between stabilizing selection,directional selection and disruptive selection. does speciation occur? what role does extinction play in speciation?


use english thanks

1 Answer

  • 1 decade ago
    Favorite Answer

    a gene pool is the complete set of unique alleles in a species or population

    factors affecting gene pool may b : random mating or fertilisation


    Stabilising selection

    -stabilizing selection usually keeps things the way they are.

    eg. number of brown rabbits is huge in the wild because selective pressure (we'll make this 'predatory fox) favours brown coat coloured rabbits over the white ones, therefore brown rabbits will have a much greater chance to live on and reproduce than the white ones.

    * The most common coat colour of rabbits therefore stays brown

    - In stabilising selection the forms at the two extremes of a continuous variation are at a selective desadvantage.

    -stabilising selection does not lead to evolution

    Directional selection

    -occurs when , a new environmental factor appears or

    a new allele appears

    - antibiotics resistance would b a good example

    (most bacteria die under treatment with antibiotics , but few with anitibiotic resistance gene in them survive and reproduce. The poplulation of antibiotic resistance bacteria therefore rises)

    - produces a change, or evolution

    Disruptive selection

    -environmental factors may change so that extremes have a selective advantage

    - usually maintains polymorphism

    There are two types of speciation

    Allopatric and sympatric

    allopatric speciation

    -involves geographical isolation

    -during period of isolation, different selction pressure may act on the isolated group

    -isolating mechanisms develop and allopatric species formed


    - polyploidy

    what role does extinction play in speciation

    well.. if , only a very few no. of individuals are isolated, the chance for them to interbreed decreases which increases the chance of thm being extinct

    Source(s): myself and wiki =]
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