AHL Content Statements

• D4.1.9

  Concept of the gene pool
  

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  A gene pool consists of all the genes and their different alleles, present in a population.
  

• D4.1.10

  Allele frequencies of geographically isolated populations

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  AOS: Students should use databases to search allele frequencies. Use at least one human example.
  

• D4.1.11

  Changes in allele frequency in the gene pool as a consequence of natural selection between individuals according to differences in their heritable traits

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  Darwin developed the theory of evolution by natural selection. Biologists subsequently integrated genetics with natural selection in what is now known as neo-Darwinism.
  

• D4.1.12

  Differences between directional, disruptive and stabilizing selection

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  Students should be aware that all three types result in a change in allele frequency.
  

• D4.1.13

  Hardy–Weinberg equation and calculations of allele or genotype frequencies

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  Use p and q to denote the two allele frequencies. Students should understand that p + q = 1 so genotype frequencies are predicted by the Hardy–Weinberg equation: p 2 + 2pq + q 2 = 1.
  If one of the genotype frequencies is known, the allele frequencies can be calculated using the same equations.
  

• D4.1.14

  Hardy–Weinberg conditions that must be maintained for a population to be in genetic equilibrium

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  Students should understand that if genotype frequencies in a population do not fit the Hardy–Weinberg equation, this indicates that one or more of the conditions is not being met, for example mating is non- random or survival rates vary between genotypes.
  

• D4.1.15

  Artificial selection by deliberate choice of traits

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  Artificial selection is carried out in crop plants and domesticated animals by choosing individuals for breeding that have desirable traits. Unintended consequences of human actions, such as the evolution of resistance in bacteria when an antibiotic is used, are due to natural rather than artificial selection.