The number of different alleles of genes in a population.
What is a population?
A population is a group of individuals of the same species that live in the same area and can interbreed.
What is a species?
A species is a group of individuals with similar characteristics that can breed to produce fertile offspring.
Natural selection is not possible without genetic variation.
What is directional selection?
An environmental change that produces a new selection pressure that favours organisms with an extreme form of a characteristic.
In directional selection the mean changes (shifting left or right on the X-axis) but the standard deviation of the sample stays the same.
What is stabilising selection?
Due to a stable environment natural selection favours the 'average' members of a population. Due to this there are more individuals at the mean so the mean doesn't change, however, the standard deviation decreases resulting in extreme characteristics being selected against preserving the mean characteristics of the population.
