A bacterium called Agrobacterium tumefasciens is used to introduce forgein genes into plant cells producing GM crop plants.
Plants can be modified to be resistant to pests, diseases and herbicides, to increase shelf life, improve flavour, increase nutrient content or to be free from certain allergens.
This could be a solution to many global issues by reducing pollution from pesticides and alleviating world hunger.
Bt is a bacterial gene often inserted into crops so that the crops produce toxins that kill insects but are harmless to humans.
It's feared that GM crops could become 'super weeds' and research has shown that gene transfer occurs between GM crops and wild plants causing genetic pollution.
Genes such as the Bt gene could increase the rate of evolution in insects resulting in insecticide-resistant insects.
GM Crops & Health
There is concern that the antibiotic resistance marker genes in GM crops might be taken up by bacteria in the human gut producing bacteria that's resistant to certain antibiotics.
Some GM crops have been made to produce drugs and vaccines - this is called pharming. This could allow cheap production of new medicines, but if these plants cross breed with food crops it could lead to contamination of food supplies and health dangers.
All releases of GMOs ares strictly regulated and require consent.
When making an application an EIA (Environmental Impact Assessment) must be submitted - this is a report on the possible environmental impacts.
This is submitted to the ACRE (Advisory Committee on Releases to the Environment) who decide whether consent should be given.
In the UK GM ingredients in food must be stated on the packaging.
Public reaction in the UK means it's unlikely that GM crops will be grown here for the forseeable future.
Protesters often destroy areas of GM research in the UK because they think that GM research is a way for big companies to make money and patent crop strains.
Potentially GM research could reduce the cost and environmental impact of farming.
Genetically modified animals - with a particular gene inserted or removed - are important for medical research.
Any animal which has gone through the addition of foreign DNA is described as transgenic.
Transgenic mice can be designed to develop certain conditions by inserting known human disease genes into their DNA.
Other mice - known as 'knockout mice' - have genes, such as tumour suppressor genes, removed.
GM animals help to create knowledge about human diseases, but there are ethical concerns such as cruelty to animals and hazzards associated with their release into the wild.
GM mosquitoes could be used to prevent the spread of malaria.