Understanding a Chromosomal formula in a karytope analysis I am reading a medical reporting results of a karyotype analysis. On it it is written: > **Chromosomal formula** > > 46,XX,del(7)(q11q36)[12]/46,XX[13] I understand that `46` is the number of chromosomes, `XX` refers to the pair of sexual chromosomes, `del(7)(q11q36)` means a deletion on the long arm of chromosome 7 spanning the bands 11 to 36. **What do`[12]` and `[13]` mean?**

Cytogenetic nomenclature is standardized in the International System for Human Cytogenetic Nomenclature. Unfortunately it is not free and my institution does not have access. However, looking at a preview of the 2013 version in Google Books, it would seem that **the number in square brackets is the number of cells scored with that karyotype**.