Mutations

• A mutation is a random change to genetic material.
• Mutations may be neutral, confer an advantage or a disadvantage.
• Mutations are spontaneous and are the only source of new alleles.
• Environmental factors, such as radiation, high temperatures and some chemicals, can increase rate of mutation.

Adaptation and Variation

• New alleles produced by mutation can result in plants and animals becoming better adapted to their environment.
• An adaptation is an inherited characteristic that makes an organism well suited to survival in its environment/niche.
• Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions.

Natural Selection

• Species produce more offspring than the environment can sustain.
• Natural selection or survival of the fittest occurs when there are selection pressures.
• The best adapted individuals survive to reproduce, passing on the favourable alleles that confer the selective advantage.
• These alleles increase in frequency within the population.

Speciation

• Speciation occurs after part of a population becomes isolated by an isolation barrier, which can be geographical, ecological or behavioural.
• Examples
  • Geographical – river, mountain, forest, earthquake.
  • Ecological — pH, salinity or different habitats.
  • Behavioural – nocturnal to diurnal, migration patterns
• Different mutations occur in each sub-population.
• Natural selection selects for different mutations in each group, due to different selection pressures.
• Each sub-population evolves until they become so genetically different they are two different species.

Topic Summary