Changing genes

• Selective breeding


  The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
• Main steps of selective breeding :

  1. Identify a desired characteristic e.g. disease resistance
  2. Select parent organisms that show the desired traits and breed them together
  3. Select offspring with desired traits and breed them together
  4. Process repeated until all offspring have the desired traits
• Main advantage of selective breeding

  Creates organisms with desirable features :

  • Crops produce a higher yield of grain

  • Cows produce a greater supply of milk

  • Plants produce larger fruit

  • Domesticated animals
• Other than agriculture, where else is selective breeding useful?

  • In medical research

  • In sports e.g. horse racing
• Disadvantages of selective breeding

  • Reduction in the gene pool (which becomes especially harmful if sudden environmental change occurs)

  • Inbreeding results in genetic disorders

  • Development of other physical problems e.g. respiratory problems in bulldogs

  • Potential to unknowingly select harmful recessive alleles
• Genetic engineering

  • The modification of the genome of an organism by the insertion of a desired gene from another organism

  • Enables the formation of an organism with beneficial characteristics
• The process of genetic engineering

  1. DNA is cut at specific base sequences by restriction enzymes to create sticky ends
  2. Vector DNA cut using the same restriction enzymes to create complementary sticky ends
  3. Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA
  4. Recombinant DNA mixed with and ‘taken up’ by target cells
• Vector

  A structure that delivers the desired gene into the recipient cell e.g. plasmids, viruses
• Benefits of genetic engineering

  • Increased crop yields for growing population e.g. herbicide-resistance, disease-resistance

  • Useful in medicine e.g. insulin-producing bacteria, anti-thrombin in goat milk

  • GM crops produce scarce resources e.g. GM golden rice produces beta-carotene (source of vitamin A in the body)
• Risks of genetic engineering

  • Long term effect of consumption of GM crops is unknown

  • Negative environmental impacts e.g. reduction in biodiversity, impact on food chain, contamination of non-GM crops forming ‘superweeds’

  • Late-onset health problems in GM animals

  • GM seeds are expensive, LEDCs may be unable to afford them or may become dependent on businesses that sell them