Satellite chromosome

In addition to the centromere, one or more secondary constrictions can be observed in some chromosomes at metaphase.

[4] The secondary constriction always keeps its position, so it can be used as markers to identify specific chromosomes.

[5] Later, Heitz (1931) qualified the secondary constriction as the SAT state (Sine Acido Thymonucleinico, which means "without thymonucleic acid"), because it didn't stain with the Feulgen reaction.

[6][7][8] The satellite at metaphase appears to be attached to the chromosomes by a thread of chromatin.

The appearance of secondary constrictions at NORs is thought to be due to rRNA transcription and/or structural features of the nucleolus impeding chromosome condensation.

Schematic karyogram of a human. Each row is vertically aligned at centromere level. The top of chromosomes 13, 14, 15, 21, & 22 are satellites, with a secondary constriction between the satellite and the centromere.
Further information: Karyotype