Genetic Engineering

Crop plants modified in this way are called genetically modified (GM) crops. The purpose is often to improve food production. Plants have been genetically engineered to resist diseases or to produce bigger, better fruits. Other GM crops resist insect attack or particular herbicides.

These changes benefit farmers in different ways:

• Disease resistance reduces losses caused by disease, leaving more healthy plants to harvest.
• Insect resistance reduces damage by insect pests and can reduce the need for chemical insecticides.
• Herbicide resistance allows a farmer to spray a suitable weedkiller without killing the crop. Removing weeds reduces competition with the crop for resources such as light, water and mineral ions.
• Improved fruit characteristics can increase the amount or quality of useful food produced.

GM crops generally show increased yields, meaning more useful crop is harvested. This can provide more food and increase farmers' income. However, the benefit depends on the characteristic introduced and the conditions in which the crop is grown: the label ‘GM’ does not itself describe what a crop can do.

Why GM crops raise concerns

A crop grows within an ecosystem, rather than in isolation. Some people are concerned that a GM crop could interbreed with related wild plants, transferring its introduced gene into wild populations. For example, herbicide resistance in wild plants could make weeds more difficult to control.

The way a GM crop is managed can also matter. If herbicide-resistant crops encourage greater use of weedkillers, populations of wild flowers may decrease. Insects that depend on those plants for food or habitat may then be affected. There are also concerns that insect-resistant crops could harm non-target insects, not just the pests the modification was intended to control.

Some people feel that the effects of eating GM crops on human health have not been fully explored. This is a concern about the adequacy of the evidence, not a demonstration that all GM food is harmful. Different modifications need to be assessed on their own evidence.

There are economic and ethical objections too. GM seeds can cost more, making them less affordable for poorer farmers. Some people question whether it is right to modify the genetic material of living organisms. An ethical objection concerns what people judge to be right or wrong; it is different from a scientific question about the likelihood of harm.

A balanced judgement therefore weighs improved food production and reduced pest damage against possible ecological effects, costs and health concerns. It considers who benefits, who could be harmed, and how strong the evidence is.

Using bacteria to make human insulin

Genetic engineering also has medical uses. Bacterial cells can be given the human gene that carries the instructions for making insulin. The modified bacteria then produce human insulin, which can be collected for use in treating people with diabetes.

The benefit comes from changing what the bacteria manufacture: they become a source of a useful human substance. The bacteria are not themselves the diabetes treatment, and producing insulin does not mean that a patient's own genome has been changed.

Research into inherited disorders

Some inherited disorders result from faulty genes. Modern medical research is exploring whether genetic modification can overcome these disorders. One approach is to introduce a working version of a gene into a patient's cells so that they can make the needed functional protein. This is an example of gene therapy.

The potential benefit is treatment of the underlying genetic problem rather than only its symptoms. It is not a guaranteed cure for every inherited disorder, however. Gene therapy can carry risks: harmful immune reactions and inflammation may occur, and some approaches have carried a risk of cancer. Improved techniques aim to reduce these dangers, but some effects may be difficult to predict.

Medical decisions must therefore weigh the likely improvement in a patient's health against the possibility and seriousness of side effects. This is a different risk assessment from judging the environmental effects of a GM crop.

Higher Tier: transferring a gene into target cells

The main steps of genetic engineering are:

1. Isolate the required gene. Enzymes are used to cut out the gene from the donor's DNA.
2. Insert the gene into a vector. A vector is a carrier, usually a bacterial plasmid or a virus. A plasmid is a small circular piece of DNA found in bacteria.
3. Use the vector to introduce the gene into the required cells. The transferred gene provides the instructions for the desired characteristic.
4. Transfer the gene at an early stage of development. As modified cells divide, their DNA is copied and passed to the cells they produce. Early transfer allows the organism to develop with the desired characteristic, rather than modifying only a small group of cells after development.

The insulin example shows the connection between these steps and their purpose: the human insulin gene is carried into bacterial cells, allowing those cells to produce human insulin. A virus can be used as a vector in other applications; a plasmid is not the only possible carrier.

The early-development principle applies when producing organisms that develop with a desired characteristic. It does not mean that all medical gene therapy must be carried out in embryos: treatments can instead target particular cells in a patient.

• GM crops: disease resistance, bigger or better fruits, insect resistance and herbicide resistance. Generally increased yields.
• GM bacteria: produce human insulin, which is collected to treat diabetes.
• Gene therapy: research into overcoming inherited disorders, for example by introducing a working version of a faulty gene into a patient's cells.

Benefits and concerns

Agriculture: more food, higher farmer income and potentially less insecticide use. Concerns include gene transfer to wild plants, effects on wild flowers and non-target insects, seed costs, and whether human health effects have been fully explored.

Medicine: useful substances and potential treatment of inherited disorders. Gene therapy can cause harmful immune reactions or other serious side effects, including a risk of cancer in some approaches.

Weigh benefits against risks and ethical objections; uncertainty does not prove harm.

Higher Tier: main steps

1. Enzymes isolate the required gene.
2. Insert it into a vector — usually a bacterial plasmid or virus.
3. Use the vector to transfer it into the required cells.
4. Transfer early in development so copied DNA passes to new cells and the organism develops with the desired characteristic.