A natural gene, whether part of DNA or isolated, occurs in nature as surely as any cell in a persons body. Cells are part of tissues and organs, and can be isolated, too. You can patent only an invention, something you created and didn't occur in nature previously. You can patent the PROCESS of isolating a gene. That is a creation, not previously occurring in nature. The same is true of a diagnostic test. A new man-made gene could be patented. But, you can't patent a discovery. You can't patent natural genes or natural DNA.