genetic diversity and adaptation

• natural selection acts on a population to to increase the frequency of advantageous alleles
• genetic diversity in a population is increased through mutations and gene flow
• gene flow- introduction of new alleles by migration
• mutation- creation of new alleles
• the change in allele frequency over time is called evolution
• mutations are changes in the gene sequence of DNA
• the selection pressure is an external factor that influences the reproductive success of an individual
• stabilising selection- natural selection favours the average phenotype e.g birth weights
• stabilising selection takes place in environments that do not change
• directional selection- natural selection favours one extreme phenotype e.g antibiotic resistance
• directional selection takes place after an environment has experienced a change
• the selection pressure in stabilising selection selects against the extreme phenotypes.
• anatomical structures are physical adaptations that have evolved to increase the chance of survival
• physiological adaptations are processes within the body that have evolved to increase a chance of survival e.g snake venom
• Shivering is a physiological adaptation that generates heat in the body. Shivering increases the chance of survival because it maintains body temperature.
• behavioural adaptations can be learnt or inherited e.g spiders have evolved to spin complex webs made of a sticky, silk thread