Biology AS Unit 2: Genetic diversity

Summary of the chapter on genetic diversity, AQA AS unit 2.

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Genetic diversity

  • Proteins make organisms different. DNA codes for proteins, so therefore, DNA determines variation. 
  • Alleles determine the characteristics of a gene. 
  • Genetic diversity is reduced when a species has fewer different alleles. 

Selective breeding:

  • Also known as artificial selection. 
  • Involves identifying individuals with the desired characteristics and using them to parent the next generation. Alleles for unwanted characteristics are bred out of the population.
  • The variety of alleles is restricted to a small number of desired alleles. This leads to a population all of which possess the desired qualities, but which has reduced genetic diversity. 
  • Plants such as wheat, the features selected for include large grains with a high gluten content, short stems and resistance to disease. 
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Genetic diversity (2)

The founder effect:

  • When a few individuals from a population colonise a new region. These few individuals carry with them only a fraction of the alleles of the population as a whole - these alleles may not be representative of the larger population. 
  • The new population will therefore have less genetic diversity. 
  • This is often seen when new volcanic islands rise out of the sea.
  • Fewer alleles means the population is less able to adapt to changing conditions.

Genetic bottlenecks:

  • When some populations of a species suffer a dramatic drop in numbers. Sometimes the reason for this is a chance event, eg volcanic eruption.
  • The few survivors will possess a much smaller variety of alleles than the original population. 
  • As the individuals breed and become re-established, the genetic diversity will remain restricted. 
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