Types of Variation
- Variation is defined as differences between individuals of the same species
- Phenotypic variation is the difference in features between individuals of the same species
- Phenotypic variation can be caused in two main ways:
- It can be genetic - controlled entirely by genes
- Or it can be environmental - caused entirely by the environment in which the organism lives
- Examples of genetic variation in humans include:
- Blood group
- Eye colour
- Ability to roll tongue
- Whether ear lobes are free or fixed
Earlobe variation diagram
Whether earlobes are attached (lobeless) or free (lobed) is an example of genetic variation
- Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle
- In this instance ‘environmental’ simply means ‘outside of the organism’ and so can include factors like climate, diet, culture, lifestyle and accidents during lifetime
- Examples include:
- An accident may lead to scarring on the body
- Eating too much and not leading an active lifestyle will cause weight gain
- Being raised in a certain country will cause you to speak a certain language with a certain accent
- A plant in the shade of a big tree will grow taller to reach more light
- Phenotypic variation can be divided into two types depending on how you are able to group the measurements:
- Continuous variation
- Discontinuous variation
Continuous Variation
- Continuous variation is when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
- Examples include height, mass, finger length etc. where there can be many intermediate groups
- Continuous features often vary because of a combination of genetic and environmental causes, for example:
- Tall parents will pass genes to their children for height
- Their children have the genetic potential to also be tall
- However if their diet is poor then they will not grow very well
- Therefore their environment also has an impact on their height
- When graphs of this data is plotted, continuous variation gives smooth bell curves (a result of all the small degrees of difference)
Continuous variation bell-shaped curve
Height is an example of continuous variation which gives rise to a smooth bell-shaped curve when plotted as a graph
Discontinuous Variation
- Discontinuous variation is when there are distinct differences for a characteristic
- For example, people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not - there are no intermediary values
- Seed shape and seed colour in peas are also examples of discontinuous variation
- Discontinuous variation is usually caused by genetic variation alone
- When graphs of these data are plotted it is presented on a bar chart
Bar chart of discontinuous variation
Blood group is an example of discontinuous variation which gives rise to a step-shaped graph