In a population of living things, the parameters of size, height, weight and colours are examples of

Analyze the question: Size, height, weight and colour are traits that differ among individuals in a population. We need to identify what type of variation these represent.

Concept: Variation within a population is of two main types:

• Continuous variation: Traits show a full range of values between two extremes, with no clear-cut categories. They are usually controlled by many genes (polygenic) and are influenced by the environment. Examples: height, weight, size, skin colour shades. Plotting them gives a bell-shaped curve.
• Discontinuous variation: Traits fall into distinct categories with no intermediates. They are usually controlled by one or two genes and are little affected by the environment. Examples: blood groups (A, B, AB, O), sickle cell status, tongue rolling, sex.

Solution:

1. Height, weight and size can take any value across a range (e.g. 150 cm, 151.3 cm, 160 cm and so on), so they are continuous.
2. Colour, in the sense of shades (for example skin or coat colour), also grades gradually from light to dark.
3. Option B (non-heritable variation) is wrong because it refers to variation caused only by the environment, and these traits have a genetic basis too.
4. Option C is wrong because it describes distinct categories, such as blood groups.
5. Option D (physiological variation) is not a standard category for these traits.

Answer: A. continuous variation

Exam tip: Ask yourself, "Can I measure it on a scale with values in between?" If yes (height, weight), it is continuous. If you can only put it in a box (blood group, sex), it is discontinuous.