One of the following is an example of discontinuous variation

1. Analyze the question You are asked to identify which trait shows discontinuous variation.

2. Explain the concept

• Continuous variation: Individuals show a full range of values between two extremes, with no clear-cut groups. It is controlled by many genes (polygenic) and is strongly affected by the environment. Examples are height, weight, skin colour/complexion, and intelligence. When plotted, the data form a bell-shaped curve.
• Discontinuous variation: Individuals fall into a few clear, distinct categories with no intermediates. It is controlled by one or a few genes and is little affected by the environment. Examples are blood group (A, B, AB, O), sex (male/female), the ability to roll the tongue, and sickle cell status (genotypes AA, AS, SS).

3. Work through the options

• A. Shape of the head: This varies gradually, so it is continuous.
• B. Blood group: You are either A, B, AB or O. There is no "in-between" blood group, so it is discontinuous.
• C. Body complexion: Complexion runs from very light to very dark with many shades between, so it is continuous.
• D. Pointed nose: This is a debatable one. Nose shape also varies in degree, so it is generally treated as continuous.

4. Answer The correct option is B. Blood group.

5. Exam tip Ask yourself: "Can I put people into clear boxes with nothing in between?" If yes, it is discontinuous (blood group, sex, tongue rolling). If you would have to measure it on a scale (height, weight, skin colour), it is continuous.