Variation (AQA GCSE Biology): Revision Note

Nature or nurture

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

• Phenotypic variation can be caused in two main ways:

  • It can be genetic – controlled entirely by genes (this is called genetic variation)

  • It can be environmental – caused entirely by the environment in which the organism lives

  • It can be due to a combination of genes and the environment

Genetic variation in humans

• Examples of genetic variation in humans include:

  • blood group

  • eye colour

  • gender

  • 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 and lifestyle

• In this instance, ‘environmental’ simply means ‘outside of the organism’

• Examples include:

  • An accident may lead to scarring on the body

  • Diet and level of physical activity affect body mass

  • Being raised in a certain country leads to speaking a certain language

  • A plant in the shade of a big 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 will pass genes to their children for height

  • Their children have the genetic potential to also be tall

  • However, if their diet is poor then they will not grow very well

  • Therefore their environment also has an impact on their height

• Another way of looking at this is that, although genes determine what characteristics are inherited, the surrounding environment will 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

• Most mutations have no effect on the phenotype as the protein that a mutated gene produces may work just as well as the protein from the non-mutated gene

• Rarely, mutations lead to the development of new alleles and so new phenotypes and if they do, most only have a small effect on the organism

• Occasionally, the new allele gives the individual a survival advantage over other members of the species

• If the new phenotype is suited to an environmental change it can lead to a relatively rapid change in the species

Example: Moth colour

• A moth develops a mutation leading to a change in its colour

• This makes it blend in better with the tree bark it lives on and less visible to predators

• This moth has a survival advantage and breeds more frequently, increasing its chances of passing on the mutated phenotype to the next generation

• The new colour quickly spreads throughout the species