17.2.3

Types of Selection Summary

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Summary of Selection Types

The three types of selection can be summarised in the following ways:

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Stabilising selection

  • Natural selection favours the average phenotype.
  • The selection pressures select against the extreme phenotypes.
  • Takes place in environments that do not change.
Illustrative background for Directional selectionIllustrative background for Directional selection ?? "content

Directional selection

  • Natural selection favours an extreme phenotype.
  • The selection pressures select against all other phenotypes.
  • Takes place after an environment has experienced a change.
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Disruptive selection

  • Natural selection favours the two extremes of a phenotype.
  • The selection pressures select against the average phenotype.
  • Takes place in an environment that favours more than one phenotype.

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1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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