Heterochromatin vs. Euchromatin: 16 Differences, Examples

Heterochromatin Definition

Heterochromatin is a tightly packed or condensed DNA that is characterized by intense stains when stained with nuclear stains, containing transcriptionally inactive sequences.

• It exists in multiple variations, up to four to five state, each of which is marked with combinations of epigenetic markers.
• The staining of heterochromatin might result in heteropycnosis; heteropycnosis is the differential staining of parts of chromosomes.
• This chromosome is different from euchromatin in that the genes in these chromosomes are usually inactivated and are not expressed.
• Heterochromatin is present in the nucleus towards the periphery. It is also not present in prokaryotic cells, indicating this form appeared later during evolution.
• However, the two most common heterochromatin include; constitutive heterochromatin and facultative heterochromatin.
• Constitutive heterochromatin usually packages the same sequences of DNA in all cells of the same species. It is usually repetitive and is present in structural forms like telomeres and centromeres.
• The genes in constitutive heterochromatin might affect the genes present near the tightly packed chromosomes.
• In humans, genes 1, 9, 16, and the Y chromosomes in men contain larger quantities of this heterochromatin.
• Facultative heterochromatin packages genes that are usually silenced through various mechanisms; however, unlike constitutive heterochromatin, facultative chromatin packages different genes in different organisms within the same species.
• The facultative chromosome is not repetitive but has the same structural components as the constitutive heterochromatin.
• The formation of facultative heterochromatin is regulated by the process of morphogenesis or differentiation.
• In humans, one of the two X chromosomes in women is inactivated as facultative heterochromatin while the other is expressed as euchromatin.
• Heterochromatin has multiple functions. Some of which include gene regulation and chromosomes integrity.
• 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.

Read Also: DNA- Structure, Properties, Types and Functions

Euchromatin Definition

Euchromatin is a more lightly packed DNA that is characterized by less intense staining and DNA sequences that are transcriptionally active or might become transcriptionally-active at some point during growth.

• Euchromatin is present towards the center of the nucleus and accounts for about 90% of the genome in an organism.
• Under an optical microscope, it appears as light-colored bands after staining. All parts of euchromatin are uniformly stained, which doesn’t result in heteropycnosis.
• Under an electron microscope, however, it appears as an elongated 10 nm microfibril.
• The structure of euchromatin can be represented as an unfolded set of beads in a string where the beads are the nucleosomes. The nucleosomes contain histone proteins that coat a particular number of DNA around.
• In euchromatin, the wrapping around by histone proteins is loose, and thus the individual DNA sequences might be accessible.
• The conformation of euchromatin is said to be controlled by a methylated part in the chromosome called histone tail.
• Euchromatin is the only confirmation of chromosomes in the case of the prokaryotic genome, which suggests that this form evolved earlier than heterochromatin.
• Unlike heterochromatin, euchromatin doesn’t exist in two forms. It only exists as constitutive euchromatin.
• Euchromatin is extremely important as it contains genes that are transcripted into RNA, which are then translated into proteins.
• The unfolded structure of DNA in euchromatin allows regulatory proteins and RNA polymerase to bind to the sequences so that the process of transcription can initiate.
• It is possible for some genes in the euchromatin to be converted into heterochromatin when they are not to be transcribed and are no longer active.
• The transformation of euchromatin to heterochromatin acts as a method for regulating gene expression and replication.
• For this purpose, some genes like housekeeping genes are always arranged in euchromatin conformation as they have to be continuously replicated and transcribed.

Read Also: Different forms of DNA- A form, B form, Z form

Key Differences (Heterochromatin vs Euchromatin)

References and Sources

• Murakami Y. (2013) Heterochromatin and Euchromatin. In: Dubitzky W., Wolkenhauer O., Cho KH., Yokota H. (eds) Encyclopedia of Systems Biology. Springer, New York, NY
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• 1% – https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/heterochromatin
• 1% – https://www.bionity.com/en/encyclopedia/Heterochromatin.html
• 1% – https://www.answers.com/Q/WHAT_IS_Heterochromatin_and_euchromatin
• 1% – https://genomebiology.biomedcentral.com/articles/10.1186/gb-2000-1-1-reports407
• <1% – https://www.biology-pages.info/C/Chromosomes.html
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• <1% – https://en.wikipedia.org/wiki/X_chromosome