Variation in the population is differences between organisms in terms of DNA sequence. The main mechanisms for variation include;

• Environmental factors

• Mutation

• Sexual reproduction

Environmental factors may influence genotypic and phenotypic diversity whilst mutation and sexual reproduction processes may increase genetic diversity. Genetic factors such as dominance, recessiveness, codominance and the other allele systems also influence phenotype.

Each individual within a species is unique in its combination of trait variations, compared to other members of a species (intraspecific variation) There are four main classes of genetic variation:

1. Morphological: internal/external shape and structure (for example, bird beaks and size)

2. Biochemical: chemical composition (proteins, carbs, fats, pigments) (for example, pigments in skin)

3. Physiological: metabolism and body processes (for example dilating blood vessels to maintain body temperature)

4. Behavioural: perception, thinking, reacting (for example, mate or court selection)