Indeed, the US Patent and Trademark Office doesn't issue patents on discoveries, only inventions that are novel and useful. But the office does grant patents to researchers who isolate plant material in the wild, create a pure form of that material that doesn't exist in nature, and then use it to treat a disease. But the process raises several ethical questions. For example, many scientists argue that much of the computer-generated research remains far too preliminary to qualify as an invention. Of course, it's difficult to draw the line, because publicly funded researchers are also filing for patents.
Researchers are most troubled by companies' push to patent expressed sequence tags or ESTs.
These genetic tags give some idea of what a DNA sequence looks like, but no more finely tuned than trying to grasp the meaning of a sentence from a few words imperfectly spelled. Companies think so. They've filed thousands of EST patent applications, often for defensive purposes. Since ESTs partially describe what a full gene might look like, they file the EST applications to prove they're working on particular genes. When they go to patent the full gene, which is far more valuable, they can use the EST application in case someone else claims to have discovered the full gene.