facultative heterochromatin


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heterochromatin

 [het″er-o-kro´mah-tin]
that state of chromatin in which it is dark-staining, genetically inactive, and tightly coiled.
constitutive heterochromatin the chromatin in regions of the chromosomes that are invariably heterochromatic; it contains highly repetitive sequences of DNA that are genetically inactive and serves as a structural element of the chromosome.
facultative heterochromatin the chromatin in regions of the chromosomes that become heterochromatic in certain cells and tissues; for example, it makes up the inactive X chromosome in female somatic cells.

fac·ul·ta·tive het·er·o·chro·ma·tin

nonrepetitive heterochromatin that comprises translatable sequences of DNA.
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