How do you make an Alzheimer's fish? To do this, first the "Tau" Alzheimer's gene must be injected into the fish larvae. In order for the egg to accept the foreign DNA into its genetic material and thereby allow the Alzheimer's gene to form, it must first be prepared—a difficult task. Because, in order to do this, a piece of the human DNA must be cloned into a so-called vector and marked with a dye. When the nerve cells of the injected fish illuminate red under the laser microscope, the researchers know that they've succeeded!