Variation and Evolution

• Three main causes of variation

  • Genetic causes
  • Environment
  • Genes & environment
• Mutations


  Random changes to DNA
• Very rarely, mutation can lead to a new phenotype
• Evolution by natural selection

  The change in the inherited characteristics of a population over time through a process of natural selection
• Selective breeding


  1. Take mixed population and select the largest male & female

  2. Breed together

  3. Offspring will be mixture of larger and smaller

  4. Select largest male & female offspring & breed together

  5. Continue doing over many generations until all offspring are large
• Problem with selective breeding: If we breed together closely related animals or plants we can get inbreeding
• Genetic engineering

  1. Identify the gene that we want to transfer

  2. Use enzymes to clone this gene

  3. Transfer gene into a smaller circle of DNA called a plasmid/virus

  4. Desired gene is transferred into the cells of the target organism

  5. Make sure all of the cells receive the transferred gene so the organism develops with the desired characteristic
• Ways to stop resistant bacteria

  • Doctors should not prescribe antibiotics inappropriately
  • Patients should complete their course of antibiotics
  • Restrict the use of antibiotics in farming
• In the 1700s, Carl Linnaeus began to classify species into different categories
• Categories for classification


  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Binomial name


  Genus & Species
• Three domain system


  • Archaea (primitive bacteria)
  • True bacteria (live in human digestive system)
  • Eukaryota