WEEK 9

• Transgenic organisms


  Genetically engineered to carry transgenes—genes from a different species—as part of their genome
• Transgenes


  • May either be a different version of one of the organism's genes or a gene that does not exist in their genome
  • Usually generated by recombinant DNA and DNA cloning techniques
• Transgenic bacteria, plants, and animals allow scientists to address biological queries and design practical solutions
• Creating a transgenic organism

  1. Selecting an appropriate technique

  2. Introducing a transgene into an organism's genome

  3. Transgene integrating randomly or at a specific site in the genome

  4. Transgenic cells multiplying and replicating the transgene

  5. Selectable marker or reporter gene included to identify successful transgene integration
• Biological methods of transgenesis


  • Virus-mediated introduction of foreign DNA into a host cell genome (transduction)
• Chemical methods of transgenesis

  • Calcium phosphate (Ca3(PO4)2) forming a precipitate to facilitate DNA binding to and entering cells
• Physical methods of transgenesis

  • Microinjection - manually inserting genetic material into cells by force
• A transgene may not integrate into the genome, and hence induce only transient expression of the researcher's gene of interest
• Transgenes introduced into animals

  1. Inserted into an early-stage, fertilized egg by microinjection

  2. Hope is for transgene to integrate into germ cells so it can be passed down through generations

  3. Offspring backcrossed to create homozygous transgenic lines
• Transgenes introduced into plants

  1. Using bacterial vector delivery (Rhizobium radiobacter) to infect plant cells and integrate transgene

  2. Cultured plant tissues on selective media to induce shoot and root growth

  3. Transgenic plants backcrossed to create high yield lines
• Practical uses of transgenic organisms

  • Agriculture (e.g. insect-resistant crops)
  • Science (e.g. research gene expression)
  • Industry (e.g. biofuel production)
  • Medicine (e.g. manufacturing human proteins)
• Genetically modified organism (GMO)

  Organism whose genome has been engineered in the laboratory to favour the expression of desired physiological traits or the generation of desired biological products
• Genetic modification techniques

  • Recombinant DNA technology (inserting genes from one organism into another)
  • Reproductive cloning (generating genetically identical offspring)
• GMOs have become a part of everyday life, entering into society through agriculture, medicine, research, and environmental management
• GMOs have benefited human society in many ways, but some disadvantages exist
• Examples of GMOs in agriculture

  • Insect-resistant crops (e.g. Bt corn)
  • Herbicide-resistant crops (e.g. glyphosate-resistant crops)
  • Nutritionally-enhanced crops (e.g. golden rice, iron-fortified rice)
• By 2014-15, about 90% of the corn, cotton, and soybeans planted in the US were GM
• By the end of 2014, GM crops covered nearly 1.8 million square km of land in more than two dozen countries worldwide, with the majority in the Americas
• Bt cotton initially successful in China

  Farmers reduced pesticide use by 50-80% and increased earnings by up to 36%
• Bt cotton grown for several years in China

  Benefits eroded as secondary pests increased, requiring more broad-spectrum pesticides
• Herbicide-resistant crops

  Enable effective chemical control of weeds, but encourage increased chemical application to soil
• To reduce risk of herbicide-resistant weeds, farmers must use multiple diverse weed-management strategies
• Golden rice

  Genetically modified to produce almost 20 times the beta-carotene of previous varieties, to combat vitamin A deficiency
• Iron-fortified rice

  Engineered to overexpress genes that enhance iron absorption and binding
• GMOs have emerged as one of the mainstays of biomedical research since the 1980s, enabling GM animal models of human genetic diseases
• Beta-carotene

  Converted to vitamin A in the human liver, accumulates in the rice endosperm to increase the amount available for vitamin A synthesis in the body
• Golden rice 2 showed a 23-fold increase in carotenoid production compared to the original golden rice plant
• Iron-fortified GM rice

  Engineered to overexpress a rice gene that produces a cysteine-rich metallothionein-like (metal-binding) protein that enhances iron absorption
• A variety of other crops modified to endure weather extremes common in other parts of the globe are also in production
• GMOs in medicine and research

  • Enabled researchers to test novel therapies and explore roles of candidate risk factors and modifiers of disease outcome
  • Revolutionized production of complex pharmaceuticals by enabling generation of safer and cheaper vaccines and therapeutics
• Pharmaceutical products from GMOs

  • Recombinant hepatitis B vaccine produced by GM baker's yeast
  • Injectable insulin (for diabetics) produced in GM Escherichia coli bacteria
  • Factor VIII (for hemophiliacs) and tissue plasminogen activator (tPA, for heart attack or stroke patients) produced in GM mammalian cells
• Edible vaccines

  Antigenic proteins produced in consumable parts of plants and absorbed into the bloodstream to stimulate immune system
• Edible vaccines could offer a safe, inexpensive, and painless way to provide vaccines, particularly in less-developed regions where refrigeration and sterile needles are problematic for traditional vaccines
• GM mosquitoes

  Express a protein that blocks entry of the malaria parasite into the mosquito's gut, disrupting the parasite's life cycle and rendering the mosquito malaria-resistant
• Sterile insect technique

  Male mosquitoes engineered with a gene that causes offspring to die before becoming sexually mature
• In field trials in a Brazil suburb, Aedes aegypti populations declined by 95 percent following the sustained release of sterile GM males
• Gene therapy

  Coupling stem cell technology with recombinant DNA methods to introduce a desired gene into a patient's stem cells, potentially curing diseases without the need for a matched donor
• Cloning is the process of generating a genetically identical copy of a cell or an organism
• Reproductive cloning

  Implantation of a cloned embryo into a real or artificial uterus, allowing it to develop into a fetus carried to term
• Somatic cell nuclear transfer (SCNT)

  Removal of the nucleus from a somatic (body) cell, insertion into an enucleated egg cell, and stimulation to begin dividing, creating a cloned embryo