What is the Difference Between Constitutive and Facultative Heterochromatin?
🆚 Go to Comparative Table 🆚The main difference between constitutive and facultative heterochromatin lies in their stability, sequence composition, and gene expression regulation. Here are the key differences between the two types of heterochromatin:
Constitutive Heterochromatin:
- Persistent and found in all cell types of a species.
- Primarily composed of large arrays of tandemly repeated (satellite) sequences.
- Mainly found at centromeric and peri-centromeric regions of chromosomes.
- Associated with distinctive histone H3 methylation and the presence of HP1 proteins.
- Genes within constitutive heterochromatin are generally poorly expressed or silenced.
Facultative Heterochromatin:
- Reversible and not found in all cell types of a species.
- Not characterized by repetitive sequences, and its DNA sequence differs from constitutive heterochromatin.
- Regions of DNA packaged in facultative heterochromatin are not consistent between cells.
- Formed during cell differentiation processes and serves as a method for gene regulation.
- Examples include X chromosome inactivation in female mammals and the formation of a sex chromatin body in cells of species with homogametic sex.
In summary, constitutive heterochromatin is a stable, repetitive sequence found in all cell types and generally silences genes within its region, while facultative heterochromatin is a reversible, non-repetitive sequence that varies between cells and plays a role in gene regulation during cell differentiation.
Comparative Table: Constitutive vs Facultative Heterochromatin
Here is a table summarizing the differences between constitutive and facultative heterochromatin:
Feature | Constitutive Heterochromatin | Facultative Heterochromatin |
---|---|---|
Definition | Regions of DNA in the chromosome found throughout the cell cycle | Regions of the DNA where the genes are silenced using certain modifications |
Location | Mainly found around the telomeric regions and peri-centromeric regions of the chromosome | Found in various regions of the chromosome and can change its location |
Appearance | Much darkly stained when visualized using the C banding technique | Less darkly stained when visualized using the C banding technique |
DNA Function | DNA codes for genes that are expressed poorly | DNA codes for genes that are expressed poorly or not at all |
Chromatin Compaction | Highly compact region of chromatin | Less compact than constitutive heterochromatin |
Histone Modifications | Histones H3 tail is di- or tri-methylated at the 9th position, attracting heterochromatin protein 1 (HP1) | Histone H3 tail is di- or tri-methylated at the 27th position (H3K27me3), characterized by the binding of Polycomb repressive complexes PRC1 and PRC2 |
Inheritance | Present throughout the cell cycle and does not code for proteins | Activated under certain conditions and is not found throughout the cell |
In summary, constitutive heterochromatin is permanently condensed and has structural roles, while facultative heterochromatin can change its location and gene expression based on specific conditions.
- Heterochromatin vs Euchromatin
- Constitutive vs Inducible Expression
- Inducible vs Constitutive Promoter
- Conditional vs Constitutive Knockout
- Chromatin vs Chromosomes
- Chromatin vs Nucleosome
- Histones vs Nucleosomes
- Histone vs Nonhistone Proteins
- Chromatin vs Chromatid
- DNA vs Histone Methylation
- DNA Methylation vs Histone Acetylation
- Structural vs Functional Genomics
- Chromatin Fiber vs Chromosome
- General vs Specific Transcription Factors
- Protoplast vs Heterokaryon
- Constitutive vs Regulated Exocytosis
- Interphase Chromatin vs Mitotic Chromosomes
- Introns vs Exons
- Obligate vs Facultative Parasite