Abstract
The y-1 mutant of C. reinhardtii tends to die or revert to wild type when grown in the dark for a long period of time. A small amount of white light (0.5 lx) enables the y-1 mutant to grow indefinitely in a near dark condition. Under this condition, the y-1 mutant is physiologically and ultrastructurally similar to the dark-grown y-1, yet remains genetically stable.