Continuous variation has a full range of values with no gaps. Discontinuous variation has a few separate groups with nothing in between.
This lesson is part of variation. The next lesson, explaining genetic and environmental contributions, looks at what causes each type.
How do you sort an example?
Use two questions. They work on any feature you meet.
- Can I measure it and get any value in a range, or does each individual fit one group?
- If I plot it, will I see a smooth curve or separate bars?
If the first answer is “any value”, the feature is continuous. If it is “one group”, the feature is discontinuous.
Worked example: eight features sorted
| Feature | Type | Reason |
|---|---|---|
| Height | Continuous | Any value between extremes |
| Body mass | Continuous | Any value between extremes |
| ABO blood group | Discontinuous | Four separate groups |
| Tongue rolling | Discontinuous | Can roll or cannot |
| Leaf length of one tree | Continuous | Wide range of lengths |
| Attached earlobe | Discontinuous | Attached or free |
| Sex | Discontinuous | Male or female |
| Seed mass of one plant | Continuous | Any value in a range |
Notice that the reason says which question you used. That sentence is what earns the mark.
Comparing the two in an answer
A comparison answer must mention both types. A one-sided statement scores less.
| Feature | Continuous | Discontinuous |
|---|---|---|
| Range of values | Full range | Distinct groups |
| Intermediate forms | Yes | No |
| Graph shape | Bell-shaped curve | Separate bars |
| Usual cause | Many genes plus environment | One gene, little environment |
| Example | Height | Blood group |
The mistake that loses marks
The common slip is to say “continuous means it changes over time”. That confuses variation with growth.
A second slip is to call a feature discontinuous just because it is counted in whole numbers. Use groups as your test: do individuals fall into a few separate groups?
Check yourself
A class records the number of petals on 40 flowers of one plant: 4, 5 or 6 petals. Another class records the height of the same 40 flowers. Sort each and give a reason.
Answer
Petal number is discontinuous: each flower has only 4, 5 or 6, with nothing in between.
Height is continuous: flowers can have any height within a range, and the values form a smooth curve.
What to study next
Move on to explaining genetic and environmental contributions. Check your sorting on the variation practice set.
If a teacher could give you fresh features to sort and explain, see online one-to-one Biology tuition.