Satellite chromosome

Besides the centromere, a secondary constriction can also be observed in some chromosomes, which would pinch off a fragment called a "satellite". A chromosome with a satellite is called a satellite chromosome or SAT chromosome. The satellite remains attached to the rest of the body of chromosomes by a thread of chromatin. The secondary constrictions are always constant in their positions and hence can be used as markers that identify particular chromosomes.

There are at least 2 SAT chromosomes in each diploid nucleus. They play a vital role in the formation of the nucleolus after cell division is completed. SAT stands for Sine Acid Thymonucleinico (without thymonucleic acid, i.e., DNA) since the chromosome on staining shows a relative deficiency of DNA in the nucleolus organizer region.

In humans, chromosomes number 13, 14, 15, 21 and 22 are examples of SAT chromosomes.