Where is centromere and short arm on Chimpanzee chromosome 21?

Be careful of the chromosome 21! If you need to work with the problems related to the location of centromeres of chimpanzee.

http://www.ncbi.nlm.nih.gov/genome/?term=chimpanzee

UCSC Genome Browser

From the recent chromosome view figures of  from NCBI or UCSC genome browser, you may not found centromere or short arm of chromosome 21 for chimpanzee. Do they have one?  Yes, surely they have.

NCBI Description for Chromosome 21

The short arm and even the centromere were not shown, maybe there are no known genes on the short arm of chromosome 21 of chimpanzee.  Therefore, the 46Mb chromosome 21 were stored in databases as 32Mb length, also viewed as only the long arm (the contig region in the figure above).

NCBI did a well job of documentation, I found this comment very helpful to understand the situation. However, the overall view for these chromosomes is misleading! As a bioinformatician, I should try to avoid such behavior during the data representation.

Finally, another misleading link I found from NCBI:

Current Assembly for Chimpanzee 

If you click on the link marked by the red arrow above, you will see chromosome 22, not 21.