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Genetically Modified

General principles

A.11.1 Define genetically modified organism (GMO).

Genetically modified organism
A plant or animal in which the DNA has been altered through the insertion of genetic material from another source. Genetic modification is most often used in agricultural crops to increase the resistance to herbicides or to engineer pesticides into crops.
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Farmer discusses advantages

A.11.2 Identify the factors underpinning (support) the genetic modification of foods.

Consider issues relating to agricultural processes (for example, enhanced yield and improved resistance to attack by pathogens), enhanced storage characteristics or enhanced eating quality.

A.11.3 Explain the principles underpinning (support) genetic modification.

Identification and isolation of the gene to be modified and introduction of the modified gene into the DNA of the crop using a vehicle for the transfer of DNA.

A.11.4 Discuss issues relating to the traceability of genetically modified crops.

"First, consumers in many countries are reluctant to buy genetically modified foods, and are sceptical of the use of GM crops for animal feed. Consequently, the concept of co-existence has been developed to separate GM and non-GM supply chains, and is only possible if all purchasers along the production chain know what they are buying. Secondly, although every GMO that is approved for commercialisation must have passed a safety assessment, it may be necessary to withdraw a certain GMO from the market - for example, if new scientific evidence raises doubts about its safety." from Wikipedia

A.11.5 Discuss the ethical issues underpinning public concerns about the safety of genetically modified foods.

How does genetic modification change the food? Are genetically modified foods safe to eat from nutritional and toxicological perspectives? Will they cause allergic reactions? What are the potential impacts on the environment? Will the genes be transferred to other organisms and what are the implications?

A.11.6 Discuss the importance of acceptance by the general public in establishing a market for a food product.

Any product must have a market to remain viable. The public are naturally wary about any new food product, and it takes time to establish a product in the marketplace. Uptake of the product must be rapid enough for the product to maintain its commercial viability.

Case study: The FlavrSavrTM tomato

A.11.7 Describe the significance of the FlavrSavr tomato.

In 1994, the first genetically modified food was approved by the FDA (US Food and Drug Administration) to go to market. The FlavrSavr tomato was modified by Calgene (a biotechnology company) using antisense technology.

A.11.8 Describe the advantages of FlavrSavr tomatoes over traditionally grown tomatoes.

Traditional tomatoes must be harvested while still green to maintain their firmness during transport to the supermarket. The tomatoes are then sprayed with ethylene to ripen them. FlavrSavr tomatoes are designed so they can ripen on the vine longer while maintaining firmer skin, thus producing a fuller-flavoured tomato on the supermarket shelves.

A.11.9 Explain how antisense technology impacts on gene expression.

Antisense RNA down-regulates the expression of specific genes. In tomatoes the enzyme polygalacturonase (PG) causes depolymerization of pectin in the cell wall of the tomato and results in softening of the ripe tomato. PG is encoded by the PG gene, which is expressed during ripening. The introduction of an antisense PG gene results in down-regulation of endogenous PG enzyme.

A.11.10 Explain how FlavrSavr tomatoes were produced.

The first step in this process involved the isolation of the PG gene from the tomato. It was then cloned using reverse transcriptase to produce antisense PG gene, which was introduced into a plasmid (a bacterial virus). The plasmid was transferred into a bacterium E. coli to multiply the number of antisense genes. The DNA was then transferred into the bacterium Agrobacterium tumefaciens, which acted as a vehicle for the transfer of the antisense PG gene into the tomato genome. In an organism with both sense and antisense mRNA, the two will encounter one another, binding due to their complementary sequences and cancelling each other out.

A.11.11 Explain how the seeds carrying the antisense PG gene were identified.

Kanamycin resistance was used as a selectable marker to identify plants carrying the antisense PG gene. Thus, only plants that have taken up the kanamycin resistance gene survive when grown in the presence of kanamycin, permitting selection of plants that have taken up the antisense PG gene.

A.11.12 Explain why kanamycin-resistant genes are approved as selectable markers for crop genetic engineering.

Kanamycin resistance genes are approved as selectable markers on grounds that the antibiotic kanamycin is no longer in use. A selectable marker is a gene inserted into a cell or organism to allow the modified form to be selectively amplified while unmodified organisms are eliminated. In crop genetic engineering the selectable marker is used in the laboratory to identify cells or embryos that bear the genetic modifications that the engineer wishes to commercialize. The selection gene is used once briefly in the laboratory but thereafter the genetically modified (GM) crop has the unused marker gene in each and every one of its cells.

A.11.13 Explain how public concerns resulted in the withdrawal of the FlavrSavr tomato from the market.

Public concern surrounded the introduction of the FlavrSavr tomato into the market. In 1997, the tomato was withdrawn from the market.

Case study: Roundup ReadyTM crops (2 hours)

A.11.14 Describe the significance of the resistance of crops to the herbicide RoundupTM.

The herbicide Roundup, which contains glyphosate as its active ingredient, works by inhibiting an enzyme (5-enolpyruvyl shikimate- 3-phosphate synthetase, EPSPS) that is necessary for the plant to synthesize particular aromatic amino acids, and thus kills the plant. Roundup ReadyTM crops, for example, genetically modified (GM) Roundup Ready soybeans, have a bacterial version of this enzyme incorporated into them, which gives them protection from the pesticide. Roundup Ready crops can then be sprayed with the pesticide, killing the weeds and leaving the crop unaffected.

A.11.15 Identify a range of crops that have been genetically modified to make them Roundup-resistant.

For example, soy beans, wheat and maize.

A.11.16 Explain how the testing of the safety of Roundup Ready crops is undertaken.

Analyse country-specific reports applying for authorisation to market Roundup Ready crops.

A.11.17 Explain the importance of independent evaluation in assessment of the appropriateness of the testing of GM crops.

Analyse critiques of the testing of GM crops.

A.11.18 Discuss the ethical issues underpinning the labelling of GM crops and their products.

Consider why producers would not want to label GM crops and their products, and why ethically it is important that they should.

References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on October 23, 2014, at 08:26 PM