A form of chromosome painting used in clinical medicine particularly for rapidly identifying the origin of accessory chromosomes or exchanges/insertions between chromosomes within the full metaphase set of chromosomes (i.e. the karyotype) of an individual. Following the principles of fluorescence in situ hybridization (FISH), the technique uses specific probes to label each pair of homologous chromosomes with a distinct combination of fluorescent markers. Spectral analysis of the resulting multicolour image reveals the abnormalities, which can often be readily visualized.