In conventional breeding, the breeder needs to observe and record the performance of the different plants and animals before selecting them and then conduct several rounds of crossing and selection to get the desired varieties or breeds. However, nowadays scientists can produce high-yielding, more nutritious crop varieties more efficiently, simply by reading the gene sequence, marking it, matching it with traits observed in the field, and by using this information, they can select thousands of individuals with desired traits in just one experiment. This process is called DNA-marker assisted selection, or MAS. It saves time.

An evolving technique

In crops, the efficiency of the selection process has been enhanced by the use of MAS. The International Maize and Wheat Improvement Centre (CIMMYT) in Mexico, where Norman Borlaug and his colleagues developed the dwarf wheat varieties of Green Revolution fame, are using MAS to develop resistance to a number of wheat diseases. The International Centre for Agricultural Research in the Dry Areas (ICARDA) in Syria is using MAS to select high-quality, drought-tolerant specimens of durum wheat, which is used to make pasta, as well as cold-tolerant varieties of lentil, and blight-resistant chickpea varieties. But MAS is often not very cost-effective and so work is under way to streamline laboratory techniques to lower costs.

Genetic modification: redrawing the map of life

Changing the genetic blueprint is somewhat analogous to writing computer codes. Lines of code define the behaviour of a program through sequences of 1 and 0. If you open a file containing such a code and cut and paste new sequences of 1 and 0 into it, the program will do something different. And if you change the DNA sequence, you may change the characteristics and behaviour of the organism it defines. In practice this is done with biotechnology tools rather than a keyboard - chemicals, bacteria and even tiny golden bullets are used to insert genes into a sequence.

More conventional forms of genetic manipulation can sometimes cross organisms that wouldn't breed together in nature. But molecular biology goes further - it can introduce genes from very different and evolutionarily distant organisms. It can thus have novel applications - such as an experiment that introduced a gene from an Arctic flounder into a strawberry so that it could briefly tolerate extremely low temperatures.

Reducing external inputs

But most GMOs are less spectacular. More typical is a successful project to make maize produce its own insecticidal protein, which would otherwise be obtained from a bacterium, Bacillus thuringiensis. This reduces the need to spray insecticide on the field. The same approach is being used with cotton and is beginning to produce real health benefits for agricultural workers, who are normally exposed to high levels of chemicals with this crop. Another example is soybeans modified to tolerate herbicides aimed at weeds.

Such maize, soybean and cotton crops are now being grown commercially. In fact, in 2001, the area planted with genetically modified crops was around 50 million hectares worldwide. Besides the United States, 14 countries are growing GMO crops, including Argentina, Australia, Canada, China, India and South Africa.

Those in favour of GMOs argue that the approach is not qualitatively different from other forms of genetic manipulation. For example, using controlled environments to cross two plants that couldn't meet in nature by other means also produces combinations of genes and characteristics that would otherwise not exist. Opponents of the technology counter that GMOs are different, because the techniques used to "edit" genes or combine genes of unrelated species could lead to undesirable traits due to unpredictable gene interactions and give rise to potential negative impacts on human health and the environment. Only time, careful research and a mass of data will resolve the dilemma of GMO safety.

March 2003