Types and sources of variation

In a nutshell

Different organisms are all very different from each other. These 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.

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.

Biology; Genetics; KS4 Year 10; Types and sources of variation

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.

Biology; Genetics; KS4 Year 10; Types and sources of variation

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.

These different versions are caused by having mutations in the DNA sequence of the gene; at some point, one base might be changed for another one. Mutations result in a change in the protein that the gene is coding for. Sometimes the protein is just different and sometimes it is faulty. Therefore, mutations can sometimes be harmless and simply provide variation but sometimes they can be harmful and impact the survival of an organism. This organism would therefore not reproduce, and the faulty mutation is not passed onto offspring in the population.

Mutations can happen for a variety of reasons:

Ionising radiation causes a change in the gene.
Chemical substances can damage or change part of a gene.
Random mistakes in DNA replication and synthesis can occur.

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.