Topic 4

• Selective breeding

  The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
• Selective breeding


  1. Identify a desired characteristic

  2. Select parent organisms that show the desired traits and breed them together

  3. Select offspring with the desired traits and breed them together

  4. Process repeated until all offspring have the desired traits
• 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 uses of selective breeding

  • 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
• Plant cloning

  • Taking plant cuttings
  • Tissue culture
• Tissue culture


  A method of growing living tissue in a suitable medium
• Growing plants using tissue culture

  1. Select a plant that shows desired characteristics

  2. Cut multiple small sample pieces from meristem tissue

  3. Grow in a petri dish containing growth medium

  4. Transfer to compost for further growth
• Ensure aseptic conditions to prevent contamination by microorganisms when preparing tissue cultures
• Growth medium

  Contains nutrients and growth hormones
• Advantages of growing plants by tissue culture

  • Fast and simple process
  • Requires little space
  • Enables the growth of many plant clones with the same desirable characteristics
  • Useful in the preservation of endangered plant species
• Disadvantages of growing plants by tissue culture

  • Reduction in the gene pool
  • Plant clones often have a low survival rate
  • Could unknowingly increase the presence of harmful recessive alleles
• Animal tissue culturing

  • Useful in the preparation of tissue samples for medical research
  • Enables the investigation of how different factors may affect a specific animal tissue, without harming the animal itself
• Preparing animal tissue cultures

  1. Extract a sample of tissue from an animal

  2. Use enzymes to separate cells within the sample

  3. Grow in a culture vessel containing growth medium

  4. Once grown, store the sample
• 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
• Genetic engineering process

  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 effects of consumption of GM crops 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
• Bacillus thuringiensis (Bt)

  • Insect larvae are harmful to crops
  • Bt is a bacterium which secretes a toxin that kills insect larvae
• Using genetic engineering to protect crops against insects

  1. The gene for toxin production in Bt can be isolated and inserted into the DNA of crops

  2. Bt crops now secrete the toxin which kills any insect larvae that feed on it
• Benefits of Bt crops


  • Increased crop yields (fewer crops damaged)
  • Lessens the need for artificial insecticides
  • Bt toxin is specific to certain insect larvae so is not harmful to other organisms that ingest it
• Risks of Bt crops

  • Long term effects of consumption of Bt crops unknown
  • Insect larvae may become resistant to the Bt toxin
  • Killing insect larvae reduces biodiversity
• Agricultural methods of increasing food production

  • Intensive farming methods e.g. 'battery' farming and the use of fertilisers and pesticides
  • Biological control
• Advantage of intensive farming

  Increases crop yields
• Disadvantages of intensive farming methods

  • Fertilisers can wash into nearby water sources and cause eutrophication
  • The use of herbicides and insecticides reduces biodiversity
  • 'Battery' farming is often seen as unethical
• Biological control

  When a new organism (often a predator) is introduced into an ecosystem to control a pest or pathogen
• Advantages of using biological control to increase food production

  • The results of biological control generally last for a long period of time
  • The effects on wildlife are less severe
• Risk of the control organism becoming a pest itself when using biological control
• • Choose parents who most strongly display the desired characteristic.
  • Breed the chosen parents.
  • From the resultant offspring (children), choose the offspring that best display the desired characteristic.
  • Breed these chosen offspring.
  • Repeat this process of breeding and re-selection over many generations until all the offspring show the desired characteristic.