Genetic modification allows us to produce plants, animals and micro-organisms with specific qualities more accurately and efficiently than through traditional methods (some examples are given below). It also allows genes to be transferred from one species to another to develop characteristics that would be very difficult or impossible to achieve through traditional breeding.
People have been breeding animals and new varieties of plants for hundreds of years to develop or avoid certain qualities. Examples include racehorses that are bred to be faster and stronger, and roses that are farmed to give us a wider range of colours and to make them more resistant to disease.
Over many generations, and for thousands of years in some cases, the world's main food crops have been selected, crossed and bred to suit the conditions they are grown in and to make them tastier. For example, cattle are bred according to whether they are for beef or dairy production. Most of today's dairy cattle are very different from the cattle that were originally domesticated, as dairy herd breeding has focused on increasing yield and improving the quality of the milk.
However, whereas traditional methods involve mixing thousands of genes, genetic modification allows just one individual gene, or a small number of genes, to be inserted into a plant or animal to change it in a pre-determined way (see an illustration). Through genetic modification, genes can also be 'switched' on or off to change the way a plant or animal develops.
For example, herbicides are used to kill weeds in fields of crops but they can also affect the growth of the crops they are intended to protect. By using genetic modification, a gene with a particular characteristic, such as resistance to a specific herbicide, can be introduced into a crop plant. When that herbicide is sprayed on the field to kill the weeds, it will not hinder the growth of the crops.
Similarly, genetic modification can be used to reduce the amount of pesticide that is used by altering a plant's DNA so that it can resist particular insect pests. Genetic modification can be used to give crops immunity to plant viruses or to improve the nutritional value of a plant. In animals bred for food production, genetic modification could potentially increase how fast they grow and to what size.