Variation: Genetic, Environmental and Combination — AQA GCSE Biology

Differences between individuals of the same species are called variation. It arises from genes, the environment, or both.

Causes of variation

There is usually extensive variation within a population of a species. It is caused by:

• Genetic causes — the different alleles an individual inherits (e.g. blood group, eye colour, natural hair colour).
• Environmental causes — the conditions an organism develops in (e.g. a scar, a language spoken, a plant grown in the shade).
• A combination of both — most characteristics (e.g. body mass, height) are affected by both genes and environment.

Source of genetic variation

Genetic variation arises from:

• Mutations — random changes to DNA (the original source of all new alleles), and
• Sexual reproduction — which mixes alleles from two parents (meiosis and random fertilisation).

Mutation and evolution

Most mutations have no effect on the phenotype. Very rarely, a mutation leads to a new phenotype; if it is advantageous in the environment, it can spread through the population by natural selection, leading to rapid change in the species.

Exam tips

• Variation is caused by genes, environment, or both.
• Most characteristics result from a combination of genetic and environmental factors.
• The source of new alleles is mutation; sexual reproduction mixes existing alleles.
• Link advantageous mutations to natural selection and evolution.