Letter H

Hetero-

Chromosomal material that is darkly staining and tightly coiled throughout the cell cycle and that is, for the most part, genetically inactive.

There are two types of heterochromatin: constitutive heterochromatin and facultative heterochromatin.

Constitutive heterochromatin is fixed and irreversible in form and function.

Chromosomes 1, 9, 16 and the Y chromosome contain regions of constitutive heterochromatin.

Facultative heterochromatin has the faculty to return to the normal euchromatic state.

The inactive X chromosome is made up of facultative heterochromatin.

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