Variation (AQA GCSE Biology): Revision Note

Nature or nurture

• Phenotypic variation is the difference in observed features between individuals of the same species

• Phenotypic variation can occur due to:

  • genetic factors: determined entirely by the DNA code

  • environmental factors; determined entirely by the environment in which the organism lives

  • a combination of genetic and environmental factors

Genetic variation in humans

• Examples of genetic variation in humans include:

  • blood group

  • eye colour

  • biological sex

  • ability to roll tongue

  • lobed or lobeless ears

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Environmental variation 

• Characteristics of all species can be affected by environmental factors such as:

  • climate

  • diet

  • accidents

  • culture

  • lifestyle

• Examples include:

  • an accident may lead to scarring on the body

  • diet and level of physical activity affect body mass

  • being raised by parents that speak a particular language is likely to result in a child speaking a certain language

  • a plant in the shade of a tree grows taller to reach more light

Genetic and environmental causes

• Some features vary because of a combination of genetic and environmental causes, for example:

  • tall parents pass height alleles to their offspring

  • their children have the genetic potential to also be tall

  • however, if their diet is low in certain nutrients then they may not reach their potential height

• Although alleles determine which characteristics are inherited, the surrounding environment may affect how these inherited characteristics develop

Genetic variation

• There is usually extensive genetic variation within a species

• All genetic variants arise from mutations

  • Mutations are random genetic changes that occur continuously

• In rare situations mutations can lead to the development of new phenotypes

• If the new phenotype aids survival after an environmental change, then the mutation may spread rapidly within a population, resulting in species change

  • This is natural selection