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A Schizosaccharomyces pombe colony in which the missegregation of a minichromosome can be observed by red sectors in a white colony. The ade6-M216 allele on the minichromosome complements the ade6-M210 deficiency at the chromosomal locus to ensure that the cells are adenine prototrophic and white. This heteroallelic complementation can no longer happen once the minichromosome is lost. As a consequence of this adenine deficiency, the cells that have lost the minichromosome accumulate an intermediate of adenine biosynthesis (P-ribosylaminoimidazole), which oxidizes to a red pigment, whereas any neighboring Ade⁺ cells remain white. Note that red Ade⁻ sectors grow more slowly than neighboring Ade⁺ sectors. This simple color-based colony-sectoring assay offers a simple, robust test for chromosome stability in S. pombe (doi: 10.1101/pdb.prot091991). Image: Professor Ursula Fleig and Professor Johannes Hegemann (Lehrstuhl für funktionelle Genomforschung der Mikroorganismen, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany).