Blood groups and tongue rolling are examples of

Analyze the question: We are asked what type of variation is shown by blood groups and tongue rolling.

Explain the concept:

• Continuous variation: There is a full range of values between two extremes, with no clear-cut categories. It is controlled by many genes (polygenic) and is often influenced by the environment. Examples are height, weight, skin colour and intelligence.
• Discontinuous variation: There are distinct, separate categories with no intermediates. It is controlled by one or a few genes and is little affected by the environment. Examples are blood groups (A, B, AB, O), tongue rolling (a person can either roll the tongue or cannot), the ability to taste PTC, and sickle cell status.

Solution:

1. Blood groups fall into clear classes: A, B, AB or O. No one is "halfway" between A and B.
2. Tongue rolling is also either/or: you can roll your tongue or you cannot.
3. Both traits are genetically determined and not changed by diet, climate or training. This rules out option C.
4. They are not graded across a range, so option A is wrong.
5. They are not specifically adaptations, so D is wrong. Neither is carried only on the sex chromosomes, so E is wrong (blood group genes are on autosomes).

Therefore, both are examples of discontinuous variation.

**Answer: B. discontinuous variation.

Exam tip: Ask yourself, "Can I measure it on a scale, or do I put it in a category?"

• Measure it (height, mass) → continuous.
• Put it in a category (blood group, tongue rolling, albinism) → discontinuous.