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Variation and natural selection (CCEA)Variation

Organisms of the same species vary in many ways. There are two types of variation – continuous and discontinuous. Natural selection explains how evolution occurs.

Part of Combined ScienceGenetics

Variation

Continuous variation

This is a gradual change in a characteristic across a population, it could be human height, mass and shoe size.

Continuous variation is represented as a .

A histogram should show normal distribution, with most individuals around the average value and a few at the extremes.

Histogram showing range of heights

Discontinuous variation

A characteristic of any species with only a limited number of possible values shows discontinuous variation. For example:

  • gender (male or female)
  • eye colour
  • blood group

Human beings have one of four blood groups, A, B, AB or O.

There are no values in between (intermediate values), so this shows discontinuous variation.

Discontinuous variation is represented as a bar chart.

Blood group graph. X-axis has blood groups A, B, AB and O. Y axis is percentage of population from 0-50.  A is just over 40%, B is just under 10 %, AB is less than 5% and O is over 45%.

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