karyosome

The karyosome is a dense aggregate of chromatin found within the nucleus of certain eukaryotic cells, particularly in some protozoa and insect cells. It is often referred to as a heteropyknotic chromosome or a supernumerary chromosome. Unlike the diffuse chromatin that forms the bulk of the nucleus, the karyosome is tightly packed and stains intensely with basic dyes. This characteristic appearance makes it readily visible under a light microscope.

The precise function of the karyosome is not fully understood and may vary depending on the organism. In some cases, it is believed to represent chromosomes that are genetically inactive or are undergoing a period of condensation. It has also been suggested to play a role in nuclear organization or as a storage site for specific genetic material. The karyosome can be a relatively stable structure throughout the cell cycle, or its appearance and size may change depending on developmental stage or environmental conditions. Its presence and morphology are often used as taxonomic features in the study of protozoa.