Variation
Exam-ready definition
Differences between individuals of the same species. Continuous variation (e.g. height) shows a complete range and is affected by many genes and environment; discontinuous variation (e.g. blood group) has distinct categories and is usually controlled by genes alone.
How this is marked
Classification questions give you a feature and ask which type. Decide by asking 'is there a full range or separate boxes?'. Mutation, meiosis and random fertilisation as causes of genetic variation is a recurring 3-marker.
In an exam answer
Classifying a feature: 'Height shows continuous variation because it has a full range of values, controlled by many genes and affected by the environment.'
Full topic guide: Inheritance