types of selection

• directional selection - individuals with a alleles for characteristics of an extreme type are more likely to survive and reproduce. might be due to an environmental change, eg. peppered moth
• stabilising selection - individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. occurs in an environment which isn't changing
• stabilising selection favours those with a stable phenotype
• directional selection favours those with an extreme phenotype
• directional selection - the mean of a population changes
• stabilising selection - the mean doesn't change but the range decreases
• stabilising selection reduces the range of possible characteristics