The following table summarizes symbols and abbreviations used in cytogenetics. Band numbers describe positions along a chromosome arm from the centromere outward; for example, 11p15.4 denotes band 15.4 on the short arm of chromosome 11.
In human genetics, the symbols are defined in the International System for Human Cytogenetic Nomenclature (ISCN). (The 2024 version of ICSN is accessible free-of-charge.)
The ISCN define two broad groups of formats:
Karyotype format, the more traditional option where locations are described at the level of arms and bands (cytogenic coordinates). Microarray format, which is originally designed for copy number change detected by a microarray using the × (times) symbol and works with genomic coordinates (numeric positions according to a certain reference genome assembly) where the start and end for each region are connected by an underscore (_). There are three levels of detail that can be used in each format:
Abbreviated system, which only looks at the level of whole chromosomes without describing any breakpoints. Short system, which includes the location of breakpoints in abnormalities using the two system's respective preferred means. Detailed/extended system, which eliminates possible ambiguities in the description of breakpoints by: For karyotype format, der (derived chromosomes) are described by listing what bands it has from pter (end of short arm) to qter (end of long arm). e terminals may be prefixed with a number if the terminal part of a different chromosome is involved. For microarray format, not only are parts that show copy number abormality shown, but also the location for neighboring normal parts. Cytogenic results may be prefixed by an abbreviation of the method used, such as ish (FISH), nuc ish (interphase FISH), arr (microarray), seq (sequencing), and ogm (optical genome mapping). Results from two ish methods can optionally add a parenthetical indicating the signal pattern using the multiplication symbol. Results from seq and ogm include specific nucleotide coordinates even in karyotype format. The ISCN documentation also describes the alternative Human Genome Variation Society (HGVS) format.
See also Chromosome abnormalities Directionality (molecular biology) for 3' and 5' notation locus (genetics) for basic notational system
References