VariationSpec 4.6.2.1
In short
Variation is the differences in the characteristics of individuals in a population. It may be due to the genes they have inherited, the conditions in which they have developed, or a combination of both. All variants arise from mutations: most have no effect on the phenotype, some influence the phenotype and very few determine the phenotype.
Differences in the characteristics of individuals in a population are called variation. Variation may be due to differences in:
- the genes they have inherited (genetic causes)
- the conditions in which they have developed (environmental causes)
- a combination of genes and the environment.
The phenotype of an organism develops from its genome and the way the genome interacts with the environment.
| Cause | Examples |
|---|---|
| Genetic | Eye colour, blood group |
| Environmental | A scar from an injury; a plant that grows poorly in poor soil |
| Both | Body mass or height: genes set a potential, but diet and lifestyle affect what is reached |
Mutations
There is usually extensive genetic variation within a population of a species. All variants arise from mutations. Of these:
- most have no effect on the phenotype
- some influence the phenotype
- very few determine the phenotype.
Mutations occur continuously. Very rarely a mutation leads to a new phenotype. If the new phenotype is suited to an environmental change, it can lead to a relatively rapid change in the species.
'Mutation' is the only source of new variants. Sexual reproduction shuffles existing alleles into new combinations, but mutations are where new alleles come from.
Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026