Heterochromatin that need not always be heterochromatic but has the faculty to return to the normal euchromatic state. The inactive X chromosome is made up of facultatative heterochromatin. When a woman transmits that X to a son, it reverts to euchromatin and genetic activity.
HETEROCHROMATIN, FACULTATIVE
Meaning of HETEROCHROMATIN, FACULTATIVE in English
English dictionary of medicine. Английский словарь медицины. 2012