Variation and evolution

• variation


  the differences in the characteristics of individuals in a population
• causes of variation


  • genes inherited
  • environment
  • genes and environment
• genetic variation


  mutation: change in DNA

  • most have no effect on phenotype
  • some influence phenotype
  • very rarely leads to a new phenotype
• evolution


  change in the inherited characteristics of a population over time through natural selection
• Theory of Evolution

  • all species have evolved from simple life forms that developed more than three billion years ago
• • organisms w/ characteristics most suited to the environment breed successfully
  • alleles are passed down to next generation
• • one population of a species can become so different they can no longer interbreed
• selective breeding

  • humans choose which organisms to breed
  • produce offspring w/ desired characteristics
• desired characteristics

  • domestic dogs -> gentle nature
  • food crops e.g. wheat -> disease resistance
  • animals -> produce more meat or milk
  • plants -> large/unusual flowers
• how selective breeding works

  1. select parents w/ desired characteristics
  2. breed together
  3. breed offspring
  4. repeat many times until all offspring have desired characteristic
• problems with selective breeding

  • inbreeding
  • inherited disease/defects
• inbreeding


  breed closely related individuals
• genetic engineering 


  modifying genetic material of an organism by introducing gene from another organism
• how genetic engineering works

  • enzyme isolates and ‘cuts out’ gene
  • transfer gene into a plasmid or virus (vector)
  • desired gene transferred into target cell
  • genes always transferred at early stage of development
• Genetically Modified crops (GM crops)

  • engineered to be resistant to insects and herbicides
  • higher yield
• advantages of genetic engineering

  • improved growth rate of animals and plants
  • increased food value of crops
  • plants resistant to herbicides and make their own pesticides
• disadvantages of genetic engineering

  • infertility genes may spread into wildlife
  • human engineering, make children look a certain way