Variation

• Variation


  Differences in the characteristics of individuals in a population
• Causes of variation


  • Differences in the genes they have inherited (genetic causes)
  • Differences in the environment in which they have developed (environmental causes)
  • Combination of genes and environment
• Mutation


  A change in a DNA sequence
• Mutations occur continuously
• Very rarely a mutation will lead to a new phenotype
• Most mutations have no or little effect
• If a new phenotype is suited to an environmental change


  It can lead to a relatively rapid change in the species
• Genetic engineering


  A process that involves changing the genome of an organism by introducing a gene from another organism to produce a desired characteristic
• Genetic engineering


  1. Cutting out the genes from the chromosomes of humans and other organisms

  2. Transferring these into the cells of different organisms
• Genetic engineering applications


  • Bacterial cells producing human insulin to treat diabetes
  • Plant crops engineered to be resistant to diseases, insects, or herbicides, or to produce bigger and better fruits and higher crop yields
• Genetically modified (GM)


  Crops that have undergone genetic engineering
• Selective breeding (artificial selection)


  The process by which humans breed plants and animals for particular genetic characteristics
• Selective breeding


  1. Choose parents with the desired characteristic from a mixed population

  2. Breed them together

  3. Choose offspring with the desired characteristic and breed them together

  4. Continue over many generations until all offspring show the desired characteristic
• Characteristics targeted in selective breeding


  • Usefulness
  • Appearance
• Examples of selective breeding


  • Disease resistance in food crops
  • Animals that produce more meat or milk
  • Domestic dogs with a gentle nature
• Selective breeding can lead to inbreeding, where some breeds are particularly prone to inherited defects or diseases
• Selective breeding reduces variation, meaning all members of a species could be susceptible to certain diseases
• Benefits of genetic engineering

  • Potential to overcome some inherited human disorders
  • Can lead to higher yields and better quality of crops
  • Crops can be engineered to be resistant to herbicides, make their own pesticides, or be better adapted to environmental conditions
• Risks and moral objections of genetic engineering

  • Genes from GM plants and animals may spread to other wildlife, which could have devastating effects on ecosystems
  • Potential negative impacts on populations of wild flowers and insects
  • Ethical concerns, for example in the future people could manipulate the genes of fetuses to ensure certain characteristics
  • Some people believe the long-term effects on health of eating GM crops have not been fully explored