Basic Nomenclature for Cytogenetics


Symbols and Abbreviations


, Separates chromosome modal number, sex chromosomes, and chromosome abnormalities

Loss of a chromosome

( ) Surround structurally altered chromosomes and breakpoints

+ Gain of a chromosome

; Separates rearranged chromosomes and breakpoints involving more than one chromosome

/ Separates cell lines or clones

// Separates recipient and donor cell lines in bone marrow transplants

del Deletion

der Derivative chromosome (used when only one chromosome from a translocation is present, or when one chromosome has two or more structural abnormalities)

dic Dicentric chromosome

dn Chromosomal abnormality not inherited from parents (de novo)

dup Duplication of a portion of a chromosome

fra Fragile site (usually used with Fragile-X syndrome)

h Heterochromatic region of chromosome

i Isochromosome (both arms of the chromosome are the same)

ins Insertion of a portion of a chromosome

inv Inversion

.ish Precedes karyotype results from fluorescence in situ hybridization (FISH) analysis

mar Marker chromosome (unidentifiable piece of chromosome)

mat Maternally derived chromosome rearrangement

p Short arm of a chromosome

pat Paternally derived chromosome rearrangement

psu dic Only one centromere is active (pseudo dicentric)

q Long arm of a chromosome

r Ring chromosome

t Translocation

ter Terminal end of arm (i.e., 2qter–end of the long arm of chromosome 2)

tri Trisomy

trp Triplication of a portion of a chromosome


General Guidelines


Modal number, sex chrom, abn abbrev (first chrom; second chrom) (arm band number; arm band number)




46 chromosomes, female (XX sex chromosomes), with a balanced translocation between chromosomes 1 and 2 with breakpoints in the short arm of chromosome 1 at band 1p32 and the long arm of chromosome 2 at band 2q22.




Modal number: total count of number of chromosomes in each cell of a given cell line

Sex chromosomes: complement of X and Y chromosomes

Band number: numerical description of the location on a chromosome arm, in order from the centromere out to the end of the chromosome. These numbers are a standard determined by the International System for human Cytogenetic Nomenclature (ISCN), revised in 2013.



UW Cytogenetic Services 
University of Wisconsin – Madison