Heterochromatin and Euchromatin

Heterochromatin and Euchromatin :

1. Heterochromatin: In eukaryotic cells some segments of the chromonema (chromosome) remain condensed during interphase and early prophase; these regions constitute heterochromatin, a term proposed by Heitz. They cluster near centromeres and telomeres (and are also scattered elsewhere), stain darkly, are two to three times richer in DNA than euchromatin, and are genetically mostly inactive because their compact packing keeps genes inaccessible to the transcription machinery.
2. Euchromatin: Euchromatin, by contrast, is the decondensed, lightly staining chromatin that is genetically active and replicates rapidly; because its DNA is more loosely packaged and accessible, euchromatin is transcriptionally active while heterochromatin is transcriptionally almost silent.