What is constitutive and facultative heterochromatin?
Constitutive heterochromatin contains genes that are stably repressed, whereas facultative heterochromatin retains the ability to convert between states.
What is the difference between constitutive and facultative?
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.
Which parts of a chromosome are always constitutive heterochromatin?
The majority of constitutive heterochromatin is found at the pericentromeric regions of chromosomes, but is also found at the telomeres and throughout the chromosomes. In humans there is significantly more constitutive heterochromatin found on chromosomes 1, 9, 16, 19 and Y.
What is facultative heterochromatin give an example?
Constitutive heterochromatin is repetitive, more condensed, and stays in this state throughout the cell cycle. An example of facultative heterochromatin is the Barr body, i.e. the inactive X chromosome in a female somatic cell.
What is facultative chromatin?
Facultative heterochromatin: Chromosome material that can be either heterochromatin or euchromatin. The inactive X chromosome is made up of facultative heterochromatin. When a woman transmits that X chromosome to a son, the chromosome reverts to the euchromatic state and to genetic activity.
What is 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.
What is the function of facultative heterochromatin?
The Latin word “facultas” literally means “opportunity.” Facultative heterochromatin (fHC) then designates genomic regions in the nucleus of a eukaryotic cell that have the opportunity to adopt open or compact conformations within temporal and spatial contexts.
What is the position of facultative heterochromatin?
Constitutive heterochromatin is present at fixed locations on chromosomes: as in centromere. Compared to this, facultative heterochromatin is in temporarily inactivated functional state as in case of one of the two X chromosomes present in cells of females.
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.
What is a facultative gene?
noun, plural: facultative genes. (1) A gene transcribed only when needed or when a cell receives a signal from its surroundings. (2) A gene whose expression is influenced by environmental factors. Supplement. Unlike constitutive gene, a facultative gene is not transcribed continually but only when needed.
What are the two main differences between constitutive 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.
Why is heterochromatin tightly packed?
The tightly packaged DNA in heterochromatin prevents the chromosomes from various protein factors that might lead to the binding of DNA or the inaccurate destruction of chromosomes by endonucleases. Besides, heterochromatin also allows gene regulation and the inheritance of epigenetic markers.
What is the difference between constitutive and facultative heterochromatin?
The type of repetitive DNA that occurs in the constitutive heterochromatin is satellite DNA, which occurs in centromeres and telomeres. On the other hand, facultative heterochromatin is a type of reversible heterochromatin, which can be condensed or decondensed based on the type of cells.
Where is constitutive heterochromatin located on a chromosome?
Constitutive heterochromatin is present at fixed locations on chromosomes: as in centromere. Compared to this, facultative heterochromatin is in temporarily inactivated functional state as in case of one of the two X chromosomes present in cells of females.
What does the facultative X chromosome look like?
Facultative X chromosome appears as a dark spot, called Barr body (or drumstick in neutrophils ) in interphase nuclei of normal females. This is to compensate presence of double dose of X chromosomes in human female genotype, when one X is enough to guide the cells.
What’s the difference between euchromatin and hetero chromatin?
Chromatin material which takes up colour differently compared to most of the chromatin (i.e. euchromatin) of the cell is called heterochromatin. During interphase, euchromatin is in hydrated and lightly coiled condition, hence lightly coloured; while during mitotic prophase, euchromatin becomes highly coiled and appears dark in colour.