GM basics

Last updated:
15 August 2012
Find out how genetic modification technology works and what it means for our food.

What is GM?

GM, which stands for 'genetic modification' or 'genetically modified', is the process of altering the genes of a plant, animal or micro-organism, or inserting a gene from another organism (living thing). Genes carry the instructions for all the characteristics that an organism inherits. They are made up of DNA (see an explanation of DNA below).

Genetic modification is achieved by altering DNA, or by introducing genetic material from one organism into another – either from a different variety of the same species or a different species altogether. For example, genes can be introduced from one plant to another plant, from a plant to an animal, or from a micro-organism to a plant. Transferring genes between plants and animals is a particular area of debate.

Sometimes the term 'biotechnology' is used to describe genetic modification. This can also have a wider meaning – that of using micro-organisms or biological techniques to process waste or produce useful compounds such as vaccines.

Why is genetic modification being used?

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.

What is DNA?

Plant cell

DNA stands for deoxyribonucleic acid. It is the genetic material contained in the cells of all living things and it carries the information that allows organisms to function, repair and reproduce themselves.

Every cell of a plant (see illustration above), micro-organism (such as bacteria), animal and human contains many thousands of different genes, which are made of DNA. These genes determine the characteristics, or genetic make-up, of every living thing, including the food we eat. When we eat any food, we are eating the genes and breaking down the DNA present in that specific food.

DNA is made up of two separate strands of what are called 'nucleotides'. These are the building blocks of DNA and are twisted around each other in a double helix structure (see illustration above). The identity of a gene and the function it performs are determined by the number of nucleotides and the particular order in which they are strung together on chromosomes – this is known as the 'sequence' of the gene. Chromosomes are the cell structures that carry the DNA.

How does genetic modification work?

Double helix structure of DNA

Genetic modification involves inserting or changing an organism's genes to produce a desired characteristic.

Inserting genes

Below is the process that takes place when a plant, for example, is modified by inserting a gene from another plant.

  1. A plant that has the desired characteristic is identified.
  2. The specific gene that produces this characteristic is located and cut out of the plant's DNA.
  3. To insert the gene into the cells of the plant that is being modified, the gene needs to be attached to a carrier. A piece of bacterial DNA called a plasmid is joined to the gene to act as the carrier.
  4. A type of switch, called a 'promoter', is also included with the gene and carrier. This helps make sure the gene works properly when it is inserted into the plant. Only a small number of cells in the plant being modified will actually take up the new gene. To find out which ones, the carrier package often also includes a marker gene to identify them.
  5. The gene package is then inserted back into the bacterium, which is allowed to reproduce to create many copies of the gene package.
  6. The gene packages are then transferred into the plant being modified. This is usually done in one of two ways.
    • It can be done by attaching them to tiny particles of gold or tungsten and firing them at high speed into the plant tissue. Gold or tungsten are used because they are chemically inert, which means they won't react with their surroundings.
    • It can be done by using a soil bacterium, called Agrobacterium tumefaciens, to take it in when it infects the plant tissue. The gene packages are put into Agrobacterium tumefaciens, which is modified to make sure it doesn't become active when it is taken into the new plant.
  7. The plant tissue that has taken up the genes is then grown into full-size GM plants.
  8. The GM plants are checked extensively to make sure that the new genes are present and are working as they should. This is done by growing the whole plants, allowing them to turn to seed, planting the seeds and growing the plant again, while monitoring the gene that has been inserted. This is repeated several times.

Altering genes
Genetic modification does not always involve moving a gene from one organism to another. Sometimes it means changing how a gene works by 'switching it off' to stop something happening. For example, the gene for softening a fruit could be switched off so that although the fruit ripens in the normal way, it will not soften as quickly. This can be useful because it means that damage is minimised during packing and transportation.

Controlling this gene 'switch' may also allow researchers to switch on modified genes, in particular parts of a plant, such as the leaves or roots. For example, the genes that give a plant resistance to a pest might only be switched on in the bit of the plant that comes under attack, and not in the part used for food.