B13: Variation and Evolution


B13.1: Variation

  • variation is the differences in the characteristics of individuals in a population
  • variation may be due to differences in the genes inherited, the conditions in which organisms develop or a combination of the genes and the environment. 
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B13.2: Evolution by Natural Selection

  • the theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed over 3 billion years ago. 
  • mutations occur continuously. very rarely, a mutation leads to a new phenotype. if the new phenotype is suited to an environmental change, it can lead to a relatively rapid change in the species. 
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B13.3: Selective Breeding

  • selective breeding is a process where humans breed plants and animals for desired characteristics. 
  • desired characteristics include:
    • disease resistance
    • increased food production in animals and plants
    • domestic dogs with a gentle nature
    • heavily scented flowers
  • problems can occur with selective breeding including defects in some animals due to lack of variation.
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B13.4: Genetic Engineering

  • crops that have had their genes modified are called GM crops. GM crops often have improved resistance to insect attack or herbicides and generally produce a higher yield. 
  • genes can be transferred to the cells of animals and plants at an early stage of development and develop the desired characteristics. this is called genetic engineering. 
  • in genetic engineering, genes from the chromosomes of humans and other organisms can be cut out using enzymes and transferred to the cells of bacteria and other organisms using a vector, which is usually a bacterial plasmid or a virus. 
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B13.5: Ethics of Genetic Technologies

  • modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders. 
  • there are benefits and risks assoiated with genetic engineering in agriculture and medicine. 
  • some people have ethical objections to genetic engineering. 
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