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close this bookBiotechnology and the Future of World Agriculture (GRAIN, 1991)
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Cutting and pasting

If the 1950s and 1960s were the decades in which scientists unravelled the basics of how genetic information is stored, multiplied and passed on from generation to generation, the 1970s and 1980s formed the period when they started harnessing techniques to move genes from one organism to another. It was the discovery of so-called 'restriction enzymes' that provided scientists with a magnificent tool. Existing in many micro-organisms, these enzymes function like genetic scissors by cutting specific gene sequences out of their surrounding DNA. Several hundreds of such enzymes have already been identified. When transferring the genetic material to a new host, the pasting work is done by another set of enzymes. By the end of the 1970s, the first commercial biotech drug produced by these cutting and pasting techniques was available. The human gene for insulin had been inserted into a bacterium and the product 'Humulin' could then be massproduced.

Having mastered the transfer of genes to micro-organisms, scientists then turned their attention to more difficult tasks: the genetic engineering of plants. Plant cells are more difficult to handle for several reasons. One is that they can contain many more genes than the relatively simple microbes. Also, unlike bacteria, they have rigid cell walls which are difficult to penetrate. Again, nature itself provided a solution. Agrobacterium tumefaciens is a bacterium that naturally infects the genetic system of plants, causing the formation of crown-gall, a common plant tumour. The trick is to remove the tumour-inducing genes from the microbe and replace them with agronomically useful ones. The genetically transformed bacterium is allowed to infect plant cells which then take up the desired genetic trait. In this way scientists already managed to introduce genes coding for insect resistance and herbicide tolerance into several crops.

A limiting factor is that normally, Agrobacterium infects only broadleafed plants, leaving some of the most important cereal crops untouched. But scientists are now studying other vectors, such as viruses, to solve this problem. The most spectacular development is the construction of a 'genegun' that blasts genetic particles directly into any host plant. The US transnational company Du Pont, has the exclusive rights, and the gun is advertised as 'easy to use and well within the capabilities of even a small laboratory.' (2) All this might sound like rather straightforward practice, but the reality is far from that. Using microbes or guns to insert a gene into specific crops is the easy part, but the real question is actually to make them work. Gene expression is still little understood. Why do genes in leaves actively promote the production of huge amounts of chlorophyll while the same genes present in roots do not?

Tremendous barriers are also faced in the genetic engineering of animals. Scientists have the opportunity to change the genetic structure of the animal at the beginning of its life - the fertilized egg or embryo. In 1982, scientists successfully transferred a gene from a rat into a mouse. The gene in question coded for a growth hormone, and when incorporated into the little rodent, it resulted in the 'mighty mouse' that reached the cover of the scientific journal Nature. The technique involved micro-injection of the genetic material into the mouse's pre-embryo, using a very thin needle. British scientists used another technique by introducing embryonic cells of a goat into the embryo of a sheep. The resulting 'geep' is made up of a mosaic of cells, some carrying the genes from one parent, and some from the other. Other techniques in animal genetic engineering use viruses or electric shocks to drive foreign DNA into animal embryos.

In practice, embryo transfer is more important than genetic engineering, at least at present. For example, the transfer of embryos from high quality cattle into lower-yielding ones is already standard practice in many countries. The advantage is obvious. In 1983 a herd of 500 pedigree Friesian cows left the UK for Egypt in four sealed flasks no bigger than suitcases. The frozen seven-day-old embryos were to be re-implanted into Egyptian cows. Where normally several ships would be needed to transport the cows, the embryos fitted on an airplane seat. Also, by inducing 'super-ovulation' in the mother cow, scientists can yield several dozens of embryos per year from a single cow that would normally produce only one. While the benefits seem spectacular, the dangers are profound as well. A future world covered with uniform, vulnerable and high-yielding Friesians - having replaced indigenous breeds in many parts of the world - is a frightening prospect indeed.

A form of genetic engineering, but normally considered as a different technology, is cell or protoplast fusion. The idea is that by mixing the cell content of different species, which normally would not cross, one can combine the genetic material. This is especially important in the medical field, where scientists have succeeded in fusing cancer cells with cells that produce antibodies that attack unwanted infectious agents. The two together form a handy combination: the cancer cell divides endlessly while the other cell produces the desired substances - monoclonal antibodies. Cell fusion is also being worked on in plants and though no major commercial results have yet materialized, the prospects are highly interesting as it offers the possibility of bringing together crop varieties with distant relatives, thus broadening available genetic variation.