Gene chips have the ability to show which genes in a cell are active at a specific time.
One of them would be a chip of the DNA from a healthy cell and the other would be the DNA from a diseased cell. The results from the healthy cell should be different from the results from the diseased cell. Those differences indicate which genes were active in each cell. This information can be used to determine the specific gene or genes that are responsible for the disease. When a liquid containing prepared complimentary DNA is poured over a gene chip, the molecules stick tightly only where the chemistry is exactly right.