Variation (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

Types of Variation

• 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

Mutation

• 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