Variation (AQA GCSE Biology: Combined Science)

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Nature or Nurture

  • Variation is defined as differences between individuals of the same species
  • 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 geneticcontrolled entirely by genes (this is called genetic variation)
    • It can be environmental – caused entirely by the environment in which the organism lives
    • Or it can be due to a combination of genes and the environment

Genetic variation

  • Examples of genetic variation in humans include:
    • blood group
    • eye colour
    • gender
    • ability to roll tongue
    • free or fixed earlobes

Earlobes, IGCSE & GCSE Biology revision notes

Whether earlobes are attached (lobeless) or free (lobed) is an example of genetic variation

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
    • Eating too much and not leading an active lifestyle will cause weight gain
    • Being raised in a certain country will cause you to speak a certain language with a certain accent
    • A plant in the shade of a big tree will grow taller to reach more light

Genetic & 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 decide what characteristics we inherit, the surrounding environment will affect how these inherited characteristics develop

Genetic Variation

  • There is usually extensive genetic variation within a population of 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
  • For example:
    • 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

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Lára

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.