Biologists typically reduce a process to its simplest form in order to identify the fundamental mechanisms driving it. Cell division is one such process, and understanding the mechanisms controlling the cell division cycle is essential for understanding human growth and development. Diseases such as cancer are characterized by cell division in which these controls have gone awry. The simplest form of cell division likely to give insight to the process in humans is that occurring in unicellular eukaryotes, such as yeast. Yeast is a general term that covers a broad range of unicellular fungi. One of the most useful species is the fission yeast, Schizosaccharomyces pombe, which has become a model system for studies of growth control and cancer genetics.