Each chromosome in the somatic-cell complement can be uniquely identified by following a number of different banding procedures. The banding patterns are highly characteristic. The International System for Cytogenetic Nomenclature (ISCN) provides schematic representations, or ideograms, of human chromosomes corresponding to approx 400, 550, and 850 bands per haploid set (1 ). Although under constant revision, its principles rest on a numbering system based on major bands as they appear from the centromere outward along each chromosome arm. Similar standards have been established for other mammalian species, and recent literature should be reviewed for appropriate standards and revisions before attempting to karyotype a metaphase specimen.
