In some sense, all crops are genetically modified through natural and artificial selection, and by selective breeding and crossing. When we talk about GMOs, however, we mean something more specific: organisms whose genetic makeup has been modified beyond what can be achieved through regular sexual reproduction. That is, the DNA of GMOs has been changed directly in the laboratory, and the results could not have been obtained through cross-breeding.
Why Create GMOs?
Part of the point of GMOs is to introduce a genetic sequence which comes from outside the species all together, and which could not be a part of the organism’s makeup in any other way. For example, DNA from a bacterium which acts as a pesticide has been included in staple food crops such as potatoes, providing those plants with their own, internal pesticide. Because potatoes cannot reproduce sexually with bacteria, other mechanisms are necessary to modify the genetic make-up of the plants. The results of these mechanisms are genetically modified organisms (GMOs).
In addition to introducing genes from outside the species, genetic modification also takes less time. Modifying an organism through sexual reproduction (cross-breeding) means waiting for several generations of the organism to reach sexual maturity, crossing and re-crossing until the desired results are achieved. When it works, genetic modification produces the desired organism within one generation. Finally, the creation of GMOs introduces only one gene (technically one “vector”, a small loop of DNA which includes the desired gene and a “promoter gene”); traditional breeding which uses sexual reproduction mixes all the genes from the parent organisms.
How GMOs are Made
Creating GMOs does not, however, necessarily involve less chance or randomness. While the makers of GMOs are able to isolate the genes in which they are interested, the techniques used to insert those genes into the organism to be modified can be difficult to control, or may have low success rates, and many attempts may be necessary.
Once the desired gene is isolated, it can either be introduced into the organism to be genetically modified in one of two ways: either using infection, or using a gene “gun”. Some plant tissue can be infected by a common bacterium which infects plants with foreign genes in the form of proteins. When plant tissue is infected, the gene is also transferred to the plant cells. In cases where this process will not work (not all plants can be infected in this way), scientists can use a gene “gun” to fire tiny microprojectiles which have been coated with the desired DNA into plant cell walls. When this works, the transformed genes must also be indentified and incubated.
Further Reading
More details about the creation, production, and marketing of GMOs, see Robert Wisner's essay, reprinted from the Tokyo Agro-Forum Bulletin, 12/19/2000, at www.econ.iastate.edu/faculty/wisner/Wisner/japan%20gmo%20900%20revised.pdf.
