# A group of students measured the hand span of 30 students in their class. They found that hand span showed a wide range of values between two extremes, with most students having a similar measurement. Another characteristic they recorded was blood group, which could only be A, B, AB or O. Explain why hand span is an example of continuous variation whilst blood group is an example of discontinuous variation.

> Cambridge International IGCSE Biology (0610) — 18.1 Variation · Explain · 4 marks

## Mark scheme (4 marks)

1. Continuous variation produces a range of phenotypes between two extremes / hand span can take any value between two extremes
2. Continuous variation is affected by both genes and environmental factors / hand span is influenced by both genotype and environment
3. Discontinuous variation can only appear in discrete / separate categories / blood group can only take a limited number of distinct values
4. Discontinuous variation is generally influenced by genes alone / blood group is determined by genes only and not by the environment

## Key terms

- [continuous variation](https://www.gradenine.co.uk/glossary/continuous-variation)
- [discontinuous variation](https://www.gradenine.co.uk/glossary/discontinuous-variation)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-group-of-students-measured-the-32cb37eb) · Published by Druglandscape Ltd.