Variation and Evolution: Continuous and Discontinuous Variation

Continuous Variation

Continuous variation involves traits that exist along a continuous scale, rather than in discrete categories.
These traits often involve the combined effect of many genes and also environmental factors polygenic inheritance.
Examples of phenotypes with continuous variation include height, weight, and skin colour.
Data for traits showing continuous variation can typically be represented on a histogram or line graph.
Natural or artificial selection can lead to shifts in the mean of traits showing continuous variation.

Discontinuous Variation

Discontinuous variation involves traits that have a defined number of possibilities.
These traits are typically controlled by a single gene or a small number of genes.
Examples of traits with discrete variation include blood group, eye colour, and inherited disorders.
Discontinuous variation does not usually show a normal distribution like continuous variation does.
Data for traits showing discontinuous variation can typically be represented on a bar chart.

Interaction between Genetic and Environmental Causes of Variation

Both genetic and environmental factors contribute to variation in a population.
Genetic variation stems from differences in genes or chromosomes.
Environmental variation can be caused by differing lifestyles, diets and experiences.
Most traits are influenced by a combination of genetic and environmental factors, with differing degrees of overlap.
Purely genetic variation is seen in traits such as blood group, while purely environmental variation is seen in traits such as language spoken.
Phenotypic plasticity refers to the ability of an organism to change its phenotype in response to changes in the environment.