Quinacrine and Giemsa-stained human metaphase chromosomes show characteristic banding patterns, and standard methods have been adopted to designate the specific patterns displayed by each chromosome. The X chromosome shown here illustrates the terminology. In the diagram, the dark bands represent those regions that fluoresce with quinacrine or are darkened by Giemsa. The short (p) arm and the longer (q) arm are each divided into two regions. In the case of longer autosomes, the q arm may be divided into three or four regions and the p arm into three regions. Within the major regions, the dark and light bands are numbered consecutively. To give an example of the methods used for assigning loci, the G6PD gene is placed at q28, meaning it is in band 8 of region 2 of the q arm. The color-blindness genes are both assigned to q27–qter. This means they reside somewhere between the beginning of q27 and the terminus of the long arm. See Chronology, 1970, Casperson, Zech, and Johansson; 1971, O'Riordan et al.; high resolution chromosome studies, human mitotic chromosomes.
Subjects: Genetics and Genomics.