heterochromatin /-krō″mətin/ [Gk, heteros, different, chroma, color] , the part of a chromosome that is inactive in gene expression but may function in controlling metabolic activities, transcription, and cell division. It stains most intensely during interphase and usually remains in a condensed state throughout the cell cycle. It consists of two types: constitutive heterochromatin, which is present in all cells and is characteristic of the Y chromosome, and facultative heterochromatin, which is present in the inactivated X chromosome of the mammalian female. Compare euchromatin. See also chromatin. −heterochromatic, adj.
