Table of Contents
What are the facultative heterochromatin?
Facultative heterochromatin is a cytological manifestation of epigenetic mechanisms that regulate gene expression. Constitutive heterochromatin is marked by distinctive histone H3 methylation and the presence of HP1 proteins, but the chromatin modifications of facultative heterochromatin are less clear.
Where is facultative heterochromatin found?
the nucleus
They are usually found in the periphery of the nucleus. It is described to be genetically inactive due to the inaccessibility to polymerases, thus, evading transcription.
What are differences between constitutive heterochromatin and facultative heterochromatin?
The main difference between constitutive and facultative heterochromatin is that constitutive heterochromatin is a permanent factor in a particular cell type, whereas facultative heterochromatin is not a permanent character of each cell of particular cell type.
Can facultative heterochromatin be transcribed?
Based on our current knowledge, the term “facultative heterochromatin” can be molecularly defined as condensed (through different mechanisms, see below), transcriptionally silent chromatin regions that decondense and allow transcription within following contexts: (1) temporal (e.g., developmental states or specific …
What is facultative heterochromatin give an example?
An example of facultative heterochromatin is X chromosome inactivation in female mammals: one X chromosome is packaged as facultative heterochromatin and silenced, while the other X chromosome is packaged as euchromatin and expressed.
What is the function of constitutive heterochromatin?
Constitutive heterochromatin on highly repeated sequences contributes to genomic stability by suppressing recombination. The centromeric and telomeric repeats are two prominent structural parts of the chromosomes that have specific pathways of chromatin modification.
Where is constitutive heterochromatin found?
(A) Constitutive heterochromatin is found at pericentromeric, telomeric, and ribosomal regions, as well as at different loci along the chromosome (B) Centromeres and pericentromeres consist of predominantly repetitive DNA sequences, including simple repeats, DNA transposons, LTR-endogenous retroviral elements, non-LTR …
What is a facultative gene?
A facultative gene is a gene which is only transcribed when needed compared to a constitutive gene. An inducible gene is a gene whose expression is either responsive to environmental change or dependent on the position in the cell cycle.
Are telomeres facultative heterochromatin?
Heterochromatin mainly consists of genetically inactive satellite sequences, and many genes are repressed to various extents, although some cannot be expressed in euchromatin at all. Both centromeres and telomeres are heterochromatic, as is the Barr body of the second, inactivated X-chromosome in a female.
What is the difference between constitutive and facultative genes?
Constitutive heterochromatin refers to the regions of DNA in the chromosome found throughout the cell cycle. Facultative heterochromatin is regions of the DNA in which the genes are silenced by modifications. Therefore, they are only activated under certain conditions and not found throughout the cell.
What is consecutive heterochromatin?
Constitutive heterochromatin domains are regions of DNA found throughout the chromosomes of eukaryotes. The majority of constitutive heterochromatin is found at the pericentromeric regions of chromosomes, but is also found at the telomeres and throughout the chromosomes.
What is considered constitutive heterochromatin?
The constitutive heterochromatin primarily encompasses the regions containing a high density of repetitive DNA elements, such as clusters of satellite sequences and transposable elements at centromeres, pericentric foci, and telomeres [3].
Which of the following is an example of constitutive heterochromatin?
For example, all human chromosomes 1, 9, 16, and the Y-chromosome contain large regions of constitutive heterochromatin. In most organisms, constitutive heterochromatin occurs around the chromosome centromere and near telomeres.