Variation (AQA GCSE Biology: Combined Science)

• 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 genetic – controlled 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

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

• 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