National 5 Biology 3.6 Evolution of Species
National 5 Biology
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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

 
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