To evolve to a malignant state, cells must acquire a broad range of novel properties: bypass normal signaling, refractiveness to apoptosis, ability to metastasize, etc. A breakdown of the mechanisms that safeguard genomic stability can be a powerful driving force to accelerate such global cell transformation. Tumors are genetically very unstable. Shown on the left is taken from a review article by Lengauer et al. In this figure, two chromosomes (red and yellow) in tumors were visualized by FISH (fluorescence labeling that can reveal individual chromosome). Most of these tumor cells lack at least one of these chromosomes (each cell should have two each). On the right is a picture showing abnormal chromosome (red) segregation in the yin6 mutant cells during anaphase. While chromosomes are separated efficiently to the two poles in wild type cells, they are not efficiently separated to the poles in the mutant. The green bar is the spindle.