types of variations

• qualitative differences in phenotypes of individuals within a population give rise to discontinuous variation
• an example of discontinuous variation is the 4 possible ABO blood groups in humans, a person can only have one of them

  results can be shown on a bar graph
• features of discontinuous variation

  distinct classes/categories

  characteristics can't be measured over a range

  individuals can't have features that fall between categories
• continuous variation occurs when there are quantitative differences in the phenotypes of individuals within a population for particular characteristics
• (continuous variation) quantitative differences do not fall into discrete categories
• (continuous variation) range of values exist between 2 extremes within which phenotype will fall e.g height and mass of a human
• features of continuous variation

  lack of categories

  presence of a range of values

  results found on a normal distribution graph
• some characteristics are controlled by a single gene known as monogenic

  characteristics usually show discontinuous variation (e.g blood group)
• other characteristics are controlled by several genes - these characteristics are known as polygenic

  characteristics usually show continuous variation (e.g height, mass)