RareShare Guide on Chromosomal Nomenclature
Publication date: 4 Jun 2025
What Are Chromosomes?
Chromosomes are thread-like structures found in the nucleus of every cell. They carry our genetic information (DNA). Humans typically have 46 chromosomes, arranged in 23 pairs.
How Are Chromosomes Labeled?
- A short arm called the p arm (from the French “petit,” meaning small)
- A long arm called the q arm (because it follows “p” in the alphabet)
- A centromere, which is the “pinched” part that separates the p and q arms
- Regions on each arm are numbered outward from the centromere (the center).
- Bands and sub-bands are subdivisions seen under a microscope when chromosomes are stained.
- The more numbers, the more specific the location.
Example: 3p22.1
- 3: Chromosome number
- p: Short arm of the chromosome
- 2: The specific region
- 2: Band within specific region
- .1: Sub-band within the larger band
|
Example |
What It Means |
|
1p36 |
Chromosome 1, short arm, band 36 |
|
7q11.23 |
Chromosome 7, long arm, band 11, sub-band 23 |
|
del(15)(q11.2q13) |
Deletion on chromosome 15, long arm, bands 11.2 to 13 |
|
dup(17)(p12) |
Duplication on chromosome 17, short arm, band 12 |
Sources:
Geer, R. C., & Messersmith, D. J. (2002). Cytogenetic Banding Nomenclature [Image]. National Institutes of Health. https://en.wikipedia.org/wiki/File:Cytogenetic_Banding_Nomenclature.png
MedlinePlus. (2021, March 26). How do geneticists indicate the location of a gene? U.S. National Library of Medicine. https://medlineplus.gov/genetics/understanding/howgeneswork/genelocation/
Mrasek, K., Schoder, C., Teichmann, A. C., Behr, K., Franze, B., Wilhelm, K., ... & Liehr, T. (2009). The hierarchically organized splitting of chromosomal bands for all human chromosomes. Molecular Cytogenetics, 2(5). https://pmc.ncbi.nlm.nih.gov/articles/PMC2636822/
ScienceDirect. (n.d.). Chromosome Band - an overview. https://www.sciencedirect.com/topics/neuroscience/chromosome-band
Nature Education. (n.d.). Chromosome Mapping: Idiograms. https://www.nature.com/scitable/topicpage/chromosome-mapping-idiograms-302
NCBI Bookshelf. (n.d.). Chromosome Map - Genes and Disease. https://www.ncbi.nlm.nih.gov/books/NBK22266/