Each chromosome arm is divided into regions, or cytogenetic bands, that can be seen using a microscope with special stains. The cytogenetic bands are labeled p1, p2, p3, q1, q2, q3, etc., counting from the centromere (the middle) out toward the telomeres (the ends). At higher resolutions, sub-bands can be seen within the bands. The sub-bands are also numbered from the centromere out toward the telomere.

Thus, if an individual gets a diagnosis of 1p36.33-1p36.32, it means that there is a deletion within chromosome 1, short arm, in region 3, band 6, and includes sub-bands .33 and .32 of region/band 36. These designations by banded chromosomes are very subjective and arbitrary and do not tell a person how large the deletion is. Microarray CGH is much more precise and tells exactly where, and how large, the deletion is.