Definition
noun
Highly condensed, tightly packed form of chromatin, as opposed to the lightly packed euchromatin
heterochromatic
adjective
Of, pertaining to, associated with heterochromatin
Supplement
Chromatin is made up of DNA, protein, and RNA. There are two forms of chromatins in the interphase nucleus: euchromatin and heterochromatin. Cytologically, heterochromatin stains more intensely than euchromatin. This indicates the tighter packing in heterochromatin than euchromatin. Heterochromatin undergoes relatively little change in the degree of condensation as it passes through the cell cycle. Another distinctive feature of heterochromatin is having a higher RNA content than euchromatin.
Heterochromatin is the tightly packed form of chromatin often found at the periphery of the nucleus. It is described to be genetically inactive. Since it is tightly packed and inaccessible to polymerases, it is not transcribed. There are different heterochromatin varieties, such as constitutive heterochromatin and facultative heterochromatin.
The main structural constituent of heterochromatin is the genetically inactive satellite DNA sequences. They are arrays of tandemly repeating, non-coding DNA. Centromeres and telomeres are examples of heterochromatic regions of chromosomes. The Barr body, which is the inactive X chromosome in a female somatic cell, is also heterochromatic.
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