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How do you read a Human Chromosome Idiogram? Molecular Biology 5 (v1 as of 1/8/06) Go to Mol Bio 5 The human chromosome IDIOGRAM (showing G-banding) can be divided into distinct regions by its banding pattern. This is an idiogram for the human X chromosome. The following logic applies to all chromosomes 1-22, and Y. The short arm is the region above the centromere and is called p and the long arm (below the centromere) is called q. (The longer arm is always shown at the bottom.) Each arm is divided into smaller regions that are further subdivided.  Different maps are presented at different resolutions, so some small bands may not show.  For instance, in the region of p11, there are subregions know as .1 to .4 and within subregion .2, there is further division into .21 to .22. In case you are confused, the column on the right is generated by reading from left to right on the left side columns A-E.  In some idiogram representations, the right column is shown without the p and q letters. (e.g. 22.1 instead of p22.1) References:  Background info: Genes V, by Benjamin Lewin, Oxford University Press, Oxford, England,1995, p782 Idiogram source: http://www.gdb.org/hugo/ Go to Mol Bio 5