Candida albicans maintains genetic diversity by random chromosome alterations, and this diversity allows utilization of various nutrients. Although the alterations seem to occur spontaneously, their frequencies clearly depend on environmental factors. In addition, this microorganism survives in adverse environments, which cause lethality or inhibit growth, by altering specific chromosomes. A reversible loss or gain of one homolog of a specific chromosome in this diploid organism was found to be a prevalent means of adaptation. We found that loss of an entire chromosome is required because it carries multiple functionally redundant negative regulatory genes. The unusual mode of gene regulation in Candida albicans implies that genes in this organism are distributed nonrandomly over chromosomes.