In medicine
The clearest single example of genetic engineering is a medicine that millions of people take every day.
Insulin
The human gene for insulin is transferred into bacteria, which then produce human insulin in fermentation tanks. Before this, insulin for people with diabetes had to be extracted from the pancreases of slaughtered cattle and pigs — in small quantities, at high cost, and not quite identical to the human protein.
Other protein medicines
Growth hormone, blood-clotting factors for haemophilia, and several others, all produced the same way.
Vaccines
A single harmless protein from a virus can be made by engineered cells and used as a vaccine, with no need to handle the live virus at all.
Diagnosis
Tests that look directly at a person's DNA can identify carriers of recessive conditions and confirm a diagnosis early.
Gene therapy
Supplying a working copy of a gene to the cells of someone with a genetic disorder. Used for a small number of conditions and still developing.
This is the answer to the disorders skill
The clotting factor a person with haemophilia lacks is a protein made by a gene. If that gene can be put into bacteria, the protein can be manufactured and given as treatment — which is exactly what is now done. The condition explained a few pages ago and the technology on this page are two halves of one story.
Treating a condition is not the same as approving of everyone having it
Being able to test for an inherited condition raises questions the biology cannot settle: who is told the result, what they do with it, and whether anyone else may see it. A test tells you about alleles. It does not tell you what anyone's life is worth, and it must never be treated as though it did.
Insulin is the standard example
The human insulin gene put into bacteria lets human insulin be made in quantity. Genetic engineering in medicine also gives vaccines, DNA-based diagnosis and, for a few conditions, gene therapy.