Definition of Facultative Heterochromatin

Facultative heterochromatin is a type of chromatin which has a tendency to interconvert itself between the heterochromatin and euchromatin. Heterochromatin is very dense as it is tightly packed and is found in the nucleus of the eukaryotic cells. The DNA present in the heterochromatin is usually inactive transcriptionally. The condensed structure of the heterochromatin does not allow the access of DNA and RNA polymerases. Consequently, replication and transcription processes are prevented.


There are two kinds of heterochromatin that are constitutive heterochromatin and facultative heterochromatin. Facultative heterochromatin is typically less than as compared to constitutive heterochromatin. It is not repetitive and has the ability to participate in transcription by losing its condensed form. The Barr body i.e. an X-chromosome which is inactive and present in the female autosome, is an example of facultative heterochromatin.


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