Variation (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

• Variation can be defined as:

Differences between individuals of the same species

• Variation gives rise to different phenotypes
• Variation can be either continuous or discontinuous

Continuous Variation

• Variation that shows a range of phenotypes
• Phenotypes fall in between extremes
• Examples include:
  • Body length
  • Body mass

Height is an example of continuous variation; it gives rise to a smooth bell-shaped curve when plotted as a frequency histogram

Discontinuous Variation

• Variation that results in a limited number of phenotypes
• There are no phenotypes that fall in between groups
• For example:
  • People are either blood group A, B, AB or O
  • Pea seeds are either round or wrinkled
  • Pea seeds are either yellow or green

Blood group is an example of discontinuous variation; it gives rise to a step-shaped bar graph

• Mutations are genetic changes
  • These changes involve alterations to the DNA
• Mutation results in the formation of new alleles
• Changes to an organism's alleles can give rise to phenotypic variation