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Definition of Heterochromatin
Medically reviewed by Min Clinic Staff | Updated: January 2026
Heterochromatin: A genetically inactive part of the genome. Heterochromatin was so named because its chromosomal material (chromatin) stains more darkly throughout the cell cycle than most chromosomal material (euchromatin). There are two types of heterochromatin: constituitive heterochromatin and facultative heterochromatin.