Chromosomal idiogram (ISCN) is a schematic diagram showing the size of a chromosome and its banding. The bands appear when stained with a chemical solution and are visible through a microscope - used to describe the location of genes on each chromosome.
Full name: International System for Human Cytogenetic Nomenclature (ISCN). Standing body - International Committee on Human Cytogenetic Nomenclature International Standing Committee on Human Cytogenetic Nomenclature. Since 1963, the official body - Cytogenetic and Genome Research
An ideogram determines the location of individual genes on chromosomes and pathologies associated with chromosomal abnormalities. A sequential numbering system that begins with its centromere is used to image genes .
Chromosomes have long and short ends (sometimes called “shoulders” or “arms”), relative to the centromere. The short end is indicated by the letter "P" from the French Petite small. The long end is indicated by the letter "Q" from the English Queue - turn, pigtail.
A small part is always indicated at the top, a large part below for the convenience of notes and comments. Each end of the chromosome is then divided into regions (regions), which are assigned their own number. The numbers of regions increase from the centromere to the telomere - p1, p2, p3, etc. at the short end, and q1, q2, q3 .... at the long end. Regions are defined by bands stained according to the Romanovsky – Giemsa method , when some parts of the chromosome are stained (G-bands), while others reject the dye (R-bands). If additional coloring reveals additional stripes within the already numbered area, then an additional digit is added, which is written through the point - p12.1, p12.2, p12.3 ... and, accordingly, q22.1, q22.2, q22.3 ...