Genetic engineering involves these steps:
Plant crops have been genetically engineered to be disease resistant or to produce bigger fruits.
Type 1 diabetes can be controlled by injecting insulin. The extra insulin allows the glucose to be taken up by the liver and other tissues, which results in cells receiving the glucose they need, and blood glucose levels staying normal.
Previously, insulin was extracted from the pancreas of pigs or cattle, but these do not have an identical composition to human insulin. Bacterial cells have been genetically modified - by inserting the human gene for insulin production into their plasmids - so that the bacteria produce human insulin.
Current genetically engineered crops include those that are resistant to insect attack or are herbicide resistant. This results in increased yields. Herbicide resistant crops allow them to tolerate herbicides sprayed on them, but weeds, which would otherwise compete with the crops are killed by it.
Scientists have recently added a gene to bananas - from a species of banana found in Papua New Guinea - that makes them produce beta carotene. This changes the colour of the flesh of the bananas to a golden-yellow colour. Beta carotene is needed by humans in order to make vitamin A, which is essential for good vision.
The advantage of golden bananas is that they could be grown and used to feed people in areas where vitamin A deficiency is common, so the bananas could help prevent blindness, and the death of many people.
Sheep and goats have been genetically engineered to produce chemicals in their milk that can be used to treat disease. In one example, the milk produced contains a protein needed to treat patients with cystic fibrosis.
Research is also exploring the possibility of providing tissues needed for transplants from animals that have been genetically engineered so that the tissues are not rejected by the human immune system.
In the future, researchers are hoping to use genetic engineering to be able to overcome some inherited disorders, such as cystic fibrosis and Huntington's disease amongst others.