Types and sources of variation

​​In a nutshell

Differences within individuals of the same species is called variation. Variation can be classed as either continuous or discontinuous and can be genetically or environmentally influenced. This summary explores the different types of variation. 

Types of variation

​​Continuous variation

Continuous variation is variation that takes place across a range. 

Examples

Height and weight.

The values of height and weight are not fixed and they can vary. Continuous variation can be plotted on a graph with a bell-shaped curve to show the distribution. 

Data in continuous variation is usually normally distributed which means that the data is symmetrically spread across the values and the graphed curve looks symmetrical. This is shown below.

​​Discontinuous variation

Discontinuous variation involves variation that takes place across specific categories. 

Example

Eye colour, hair colour or blood group. There are a limited number of categories that these characteristics belong to. So, an individual can only have a blood group that falls into a set category.

Discontinuous variation can only be plotted in diagrams with discrete categories, with no way to link the categories to each other. 

Sources of variation

​​Genetic variation

Variation in an organism's characteristics can be due to the genes it has inherited. Half an organism's genes are from their mother and half are from their father. Inherited genetic variation comes from having different alleles; these are different versions of the same gene. 

Example

Eye colour is solely determined by genes. One allele of the genes that code for eye colour might produce blue eyes, whereas another allele might produce brown eyes. 

​​Environmental variation

Variation can also come from environmental factors. This is when characteristics are affected by the surroundings such as the weather, the food we eat, the hobbies we take part in or even events we experience growing up.

Example

A scar from a wound that is produced by an environmental factor such as falling off your bike.

Overlapping genetic and environmental variation

Some variation can be partly genetic and partly environmental. Sometimes genetics influence a characteristic more than the environment, and vice versa. It is not always clear cut what influences variation of a characteristic the most.

Example

Height can be inherited from parents: two tall parents are likely to have a tall child. However, it can also be environmentally affected. If a child does not receive the right nutrition, their growth will be stunted and they won't be very tall.