Causes of variation
Genetic
Genetic variation exists because of changes to chromosome Genetic structures that usually occur in functional pairs in the nucleus of cells (except gametes and bacteria). or geneA short length of DNA that codes for a particular characteristic. (DNA).
mutationA random and spontaneous change in the structure of a gene, chromosome or number of chromosomes. are random changes in the number of chromosome Genetic structures that usually occur in functional pairs in the nucleus of cells (except gametes and bacteria). (e.g. Down syndrome) or the structure of a gene (e.g. cystic fibrosis).
The random nature of sexual reproduction also gives rise to variation.
Environmental variation
An individual’s environment can also cause variation.
For example, human height is genetically controlled but actual height reached will depend on the nutrition available.