Example 1 - Rice
In many places across the world, expecially in developing countries, the population relies on rice as its food source.
However, rice doesn't contain much vitamin A, and so people often have a deficiency of this vitamin.
To solve the problem, rice can be genetically engineered to provide humans with vitamin A.
This is done by taking a gene that controls beta-carotene production from carrot plants and inserting it into rice plants.
Humans can then change the beta-carotine into vitamin A, and the deficiency problem is solved.
Example 2 - Human Inslulin
For humans with diabetes, insulin can be a bit of a problem.
So, to provide the insulin treatment required, genes that make human insulin can be inserted into bacteria.
This means that the bacteria produces human insulin.
Then, when the bacteria reproduces on a large scale, we have lots of bacteria making human insulin.
This is then taken from the bacteria and is used to treat diabetes.
Example 3 - Herbicides
Some plants have herbicide resistance, but others don't.
If we need a plant to have herbicide resistance, like a crop, we can do the following.
We can take the gene from a herbicide-resistant plant, e.g. a nuisance weed, and insert it into a crop.
Then, when the crop reproduces, there are lots of herbicide-resistant crops being created.
This means that herbicides can be sprayed on weeds near these crops, and only the weeds will die.
This is great for farmers worldwide.