AQA GCSE Biology

Revision Notes

6.2.1 Variation

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

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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