Genetic and environmental variationSpec 3.33
In short
Variation is the differences between individuals of the same species. It can be genetic, caused by the alleles inherited, such as blood group and eye colour, or environmental, caused by surroundings and way of life, such as a scar. Many features depend on both: a person's height depends on their alleles and on their diet.
Differences between individuals of the same species are called variation. Variation within a species can be genetic, environmental, or a combination of both.
| Genetic variation | Environmental variation | |
|---|---|---|
| What it is | Differences caused by the alleles an organism inherits | Differences caused by an organism's surroundings and way of life |
| Examples | Blood group, eye colour, sex | A scar, body mass affected by diet, plant height affected by light |
Many features are affected by both. For example, a person's height depends on the alleles they inherit and also on their diet when growing up. A plant's height depends on its alleles, and also on the light and minerals it receives.
Identical twins have the same alleles. Differences between them must be caused by the environment, which is a favourite way of testing this point.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026