What is the difference between constitutive and facultative heterochromatin?

Constitutive heterochromatin:

Heterochromatin refers to the regions of DNA in the chromosome found throughout the cell cycle.

Facultative heterochromatin:

The regions of the DNA where the genes are silenced using certain modifications are referred to as facultative heterochromatin.

Differences between constitutive and facultative heterochromatin:

Constitutive heterochromatin	Facultative heterochromatin
They are mainly found around the telomeric regions and peri-centromeric regions of the chromosome.	They are only activated under certain conditions and are not found throughout the cell.
2. Constitutive heterochromatin regions are visualized using the C banding technique.	2. The facultative heterochromatin is a silenced gene that is expressed only under specific conditions.
3. The constitutive heterochromatin appears to be much darkly stained.	3. DNA codes for genes that are expressed poorly.