Variation — Genetic and Environmental

Variation is the differences that exist between individuals. This lesson covers the causes of variation, the distinction between genetic and environmental variation, and how these concepts relate to evolution. This is a key topic in the AQA GCSE Combined Science Trilogy specification (8464).

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What Is Variation?

Variation means the differences between individuals of the same species. No two organisms are exactly alike (except identical clones). Variation can be classified as:

1. Genetic variation — caused by differences in DNA
2. Environmental variation — caused by conditions in which an organism lives
3. A combination of both — most characteristics are influenced by genes AND the environment

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Genetic Variation

Genetic variation arises from differences in DNA. It is inherited from parents to offspring.

Sources of Genetic Variation

Source	How It Causes Variation
Meiosis	Produces gametes with different combinations of alleles due to independent assortment and crossing over
Random fertilisation	Any sperm can fertilise any egg, producing unique combinations of alleles
Mutations	Random changes in the DNA base sequence can create new alleles