Discrete variation
Characteristics controlled by a single gene (one copy inherited from each parent) tend to have phenotypes that fall into separate categories. They show discrete variation.
Discrete variation in a group of individuals can be shown using a bar chart. The table gives some other examples of characteristics that show Variation that is clear cut and observable; sometimes referred to as dicontinuous..
| Characteristic | Possible phenotypes |
| Hand used for writing | Left or right |
| Ability to roll tongue | Yes or no |
| Snapdragon petal colour | Red, white or pink |
| Characteristic | Hand used for writing |
|---|---|
| Possible phenotypes | Left or right |
| Characteristic | Ability to roll tongue |
|---|---|
| Possible phenotypes | Yes or no |
| Characteristic | Snapdragon petal colour |
|---|---|
| Possible phenotypes | Red, white or pink |
Continuous variation
Most characteristics are controlled by more than one gene and are described as being The type of inheritance determined by the interaction of several genes acting together eg skin colour..
Polygenic characteristics have phenotypes that can show a wide range of values, with each value following on from the value before. This is described as Variation that shows a wide range of intermediate values between two extremes;they can be measured..
Continuous variation in a group of individuals can be shown using a histogram.
The table gives some examples of characteristics that show continuous variation.
| Characteristic | Possible phenotypes |
| Height | Wide range of values, eg 1.69m |
| Body mass | Wide range of values, eg 58kg |
| Circumference of left wrist | Wide range of values, eg 15cm |
| Milk yield of cow | Wide range of values, eg 7500 litres/year |
| Root length of plant | Wide range of values, eg 5cm |
| Characteristic | Height |
|---|---|
| Possible phenotypes | Wide range of values, eg 1.69m |
| Characteristic | Body mass |
|---|---|
| Possible phenotypes | Wide range of values, eg 58kg |
| Characteristic | Circumference of left wrist |
|---|---|
| Possible phenotypes | Wide range of values, eg 15cm |
| Characteristic | Milk yield of cow |
|---|---|
| Possible phenotypes | Wide range of values, eg 7500 litres/year |
| Characteristic | Root length of plant |
|---|---|
| Possible phenotypes | Wide range of values, eg 5cm |
Many phenotypes are also affected by environmental factors, such as the conditions to which the individual has been exposed. For example, a person's height is determined by the genes they have inherited and by the availability of food when they are growing.
