Features controlled by several genes
Definition
Polygenic inheritance
The control of a single characteristic by several genes acting together.
- Polygenic inheritance is when a feature is controlled by several genes working together.
- Many everyday features, such as height, skin colour and eye colour, are polygenic.
- Each of the genes adds a small effect, and together they set the feature.
Example
Human height is affected by many genes, so people range through every height rather than being simply tall or short.
Note
Most features are polygenic; features controlled by a single gene are the exception.
Polygenic features and variation
Definition
Continuous variation
Variation that produces a continuous range of phenotypes between two extremes, with no distinct categories.
- Because many genes each add a little, polygenic features vary smoothly across a range.
- This smooth range is called continuous variation, with no distinct categories.
- A feature controlled by a single gene tends to fall into a few clear categories instead.
- The environment can also affect polygenic features, widening the range further.
Hint
A smooth range points to many genes; a few distinct categories point to a single gene.
Common Mistake
Do not treat a feature like height as controlled by one gene: it is polygenic.
Self review
- What is polygenic inheritance?
- Give two examples of polygenic features.
- What is continuous variation?
- How can you tell a polygenic feature from a single-gene feature?
