By Tim Radford / The Guardian & The Observer / Tuesday February 16, 1999
DNA is the code of life: an "alphabet" of four acids common to every living creature. If DNA is the alphabet, genes are the phrases and sentences written in that alphabet.
A gene is a string of code that tells the cells to make the proteins and behave in a certain way that adds up to a characteristic which can be passed on to the next generation. There is a tiny genital microbe with about 450 genes. Humans are made up of 70,000 to 100,000 genes.
Some genes seem to be common to almost all life (scientists who took the yeast microbe to bits were very surprised to find it appeared to have the gene for human breast cancer and human colorectal cancer - but then that's probably because humans descended from yeasts in the first place)
Humans began moving genes around inside other forms of life the moment they invented agriculture. Modern wheats, fruits and vegetables are monstrously unlike their wild progenitors because generations of farmers have selected the genes for bigness, or juiciness, or sweetness or high protein, or sturdy stalks and so on.
But the traditional genetic engineers moved genes around thousands at a time, by trial and error. The discovery of how DNA works in 1953 created a new world: genes can now be selected in one plant or animal, and then transferred and switched on in another. Or they can be identified and cancelled, slowed down or speeded up.
There are now laboratory mice with human immune systems, pigs with "human compatible" hearts and tobacco plants with jellyfish luminescence genes.
But the big money is in crops proof against herbicide - so that one spraying kills off all the competition - or crops with their own built-in insect resistance. But these are the crops which worry environmentalists: how will they affect the natural life around them? And what will food from such plants do to humans when they become a part of the standard diet?
There is no way of answering either question simply: there could be hundreds of GM foods, all from entirely different gene adjustments. Even if one of them is proved safe - after a lifetime of human consumption - what does that say about the others? And if a consumer does die after many years of consumption, how will anyone be sure it was the GM food, and not the crisps, the hot dogs, the beer or the cigarettes? Can resistance genes escape into wild plants? Probably. Will it happen on a massive scale? So far, the answer is probably not. Will the world eventually be over-run by superweeds? Who knows: the alternative scenario painted by environmentalists is that the effect of herbicide resistant crops will be to kill off all the weeds, and with them the birds and insects that depend on them, turning farmland into sterile monocultures.
This is a hot topic precisely because nobody can throw much convincing light on these questions. The honest answer is watch this space.
