The other chromatin.

Current understanding of heterochromatin, thanks to molecular data, focuses on its performing several functions in evolution and development. Heterochromatin shows characteristic distribution patterns in karyotypes and contributes to the broad scattering of genome sizes through biological taxa. Heterochromatin remains compacted and thus different from properly stained euchromatin during somatic interphase. A minimum amount of heterochromatin, however, is required for it to be visible in light microscopy. It may further escape notice during the dynamic processes of embryogenesis and gametogenesis. Present-day biology is in search of specific proteins and DNA sequences that comprise heterochromatin. The data that result from overcoming the threshold of visibility will support understanding of interference by heterochromatin in ontogeny and evolution. The contributions of Sigrid and Wolfgang Beermann to the study of heterochromation diminution (DNA elimination) are recalled, and we also discuss the functions and effects of heterochromatin on differential DNA endoreplication and in speciation.