Which of the following is an example of continous variation?

1. Analyze the question You are asked to pick the trait that shows continuous variation.

2. Explain the concept

• Continuous variation: a trait that shows a full range of values between two extremes, with no clear-cut groups. It is usually controlled by many genes (polygenic) and is also influenced by the environment. You measure it, and a graph of it gives a bell-shaped curve. Examples: height, weight, skin colour, intelligence.
• Discontinuous variation: a trait that falls into distinct categories with no in-between forms. It is usually controlled by one or a few genes, and the environment has little effect. You count it. Examples: blood groups, sex, haemoglobin type (AA, AS, SS), tongue rolling.

3. Solution: test each option

• A. Human blood groups: A, B, AB, O are distinct categories, so this is discontinuous.
• B. Sex difference in humans: a person is male or female, with no gradation, so this is discontinuous.
• C. Haemoglobin types: AA, AS, SS, AC and so on are distinct types, so this is discontinuous.
• D. Height in humans: people can be 150 cm, 151.3 cm, 165 cm, 180 cm, and every value in between. It is a measurable range, so this is continuous.

4. Answer **D. Height in humans.

5. Exam tip Ask yourself: "Do I measure it or count it in categories?"

• Measure on a scale → continuous (height, weight)
• Put in a box → discontinuous (blood group, sex, haemoglobin type)

Well done for working through this carefully. Keep practising questions like this and you will pick them up quickly.