What are GMOs?

Cells and DNA

Living things are made of building blocks called cells – this helps to understand genetic modification (GM). Higher animals are made up of hundreds of thousands of cells (many of which are specialised, such as muscle cells and nerve cells) while bacteria consist of a single cell. At the centre of each cell are long chains of a complex chemical, known as DNA (deoxyribonucleic acid). These DNA chains form the genetic material of the cell. The information encoded on DNA is sub-divided into blocks known as genes.


All living organisms – animals, plants and micro–organisms (such as bacteria or fungi) – carry copies of all their genes in their cells. Those genes hold the information that determines the organism's particular form and function. Specific characteristics of an organism may be linked to particular genes or combinations of genes. Genetically modified organisms (GMOs), therefore, are organisms whose genes have been artificially altered to modify their characteristics in some way or another. For example, medicinal products such as insulin, blood factor VIII and human growth hormone were formerly produced from humans and animals and some carried a slight risk of transmitting disease. Now, with the use of GM technology, pure and safe equivalents can be produced using GMOs and industrial scale quantities are possible by growing such modified bacteria on a large scale in fermenters.

Genetic modification

GM is the process of altering the genetic material of an organism by use of a method that does not occur in nature. Often GM involves isolating and removing the DNA encoding a single gene from one organism, manipulating it outside the cell (in a laboratory) and reinserting it into the same organism or into the genetic material of another organism. The aim of GM is often to introduce a new or altered characteristic to the target organism.

GMOs may be plants, animals or (most commonly) micro-organisms (including bacteria, viruses parasites and fungi). Where the GMO is a micro-organism it is typically referred to as a genetically modified micro-organism (GMM). An important point to note about GMOs is that in the case of humans, even if they have undergone genetic modification as a result of, for example, gene therapy, they are not regarded as GMOs in HSE's legislation. A GMO that is a plant or an animal can be referred to as a larger GMO (LGMO).

What is 'contained use'?

The term 'contained use' covers any activity involving GMOs where control measures, such as physical, chemical or biological barriers, are used to limit contact between GMOs and humans or the environment so as to provide a high level of safety. It relates to the actual process of GM, and also to the use, storage, transport and destruction of GMOs. Typical contained use facilities would be microbiology laboratories, animal houses, plant growth rooms and glasshouses, industrial fermenters used for large scale production of enzymes or therapeutics, and facilities to contain genetically modified farm animals.

GMOs that are deliberately introduced into the environment for experimental purposes, or placed on the market, for example, as food or for medicinal purposes, are obviously not contained. They are outside the scope of the Regulations on contained use and regulated under other legislation.

The vast majority of work with GMOs in contained use is inherently safe. This is because most work involves the insertion of genes into micro-organisms that have been deliberately 'crippled' with disabling mutations so that they will not grow outside of the controlled environment of a laboratory test tube. Safety is thus built into the experimental design. However, a small number of activities involve GMMs that are not disabled and still capable of growth outside of the laboratory. It is, therefore, very important to assess the risks of all activities and make sure that any necessary controls are put in place to protect people and the environment.

Risk assessments for such work must be submitted to the regulatory authorities for approval before work can commence. The regulatory authorities are thus in a position to ensure that the work is carried out in facilities and equipment that contain the infectious materials during the work activities. The assignment of these containment measures tends to be done on a precautionary basis to allow some margin of safety, where there is any uncertainty over the risks. Gradually, as knowledge increases, some precautionary safeguards are being removed, where there is clear evidence that they are not necessary, and efforts are being focused on ensuring the safety of those projects where there are tangible hazards. The safety record in this industry is extremely good.

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Updated 2021-05-05