Euchromatin vs Heterochromatin

Let’s know about Euchromatin vs Heterochromatin. Euchromatin and heterochromatin are the two ways in which chromatin can be found, a substance that represents the base of chromosomes. It is found inside the nucleus of cells and its main function is to preserve and transmit the genetic information contained in DNA, as well as to carry out protein synthesis.

This complex is found only in eukaryotic cells, that is, in cells with a defined nucleus. Prokaryotic cells have a different organization of their DNA. Chromatin has a great potential for compaction thanks to histones, the main component in its structure that compresses genetic material.

Euchromatin vs Heterochromatin
Euchromatin vs Heterochromatin

This process is carried out in different ways depending on the degree of transcription, it also fixes its position to improve replication processes and, if necessary, to repair DNA for the proper functioning of the cell. .


It is defined as the most compact expression of chromatin, does not change its level of compaction throughout the cell cycle.It is composed of highly repetitive and inactive DNA sequences that do not replicate and form the chromosome centromere.

Its function is to protect the integrity of the chromosome due to its dense compaction and to regulate genes.

It can be identified with an optical microscope with a dark color due to its density. Heterochromatin is divided into two groups:


It appears to be highly condensed by repetitive sequences in all cell types and cannot be transcribed because it does not carry genetic information. They are the centromeres and telomeres of all chromosomes that do not express their own DNA.


It differs in different cell types in that it only condenses in certain cells or specific periods of cell development, such as Barr’s corpuscle, which is formed because the heterochromatin of the facultative contains active regions that may under certain conditions and characteristics can be transferred under It also includes satellite DNA. (Euchromatin vs Heterochromatin)


Euchromatin is the part of chromatin that remains in a less condensed state than heterochromatin and is distributed throughout the cell cycle.It represents the active form of chromatin in which the genetic material is being transferred. Its low condensed state and its ability to change dynamically make transcription possible.

Not all euchromatin is transferred, however, the rest of it is usually converted to heterochromatin, to compress and preserve natural information.

Its structure is similar to that of a pearl necklace, where each pearl represents a nucleosome composed of eight proteins called histones, around which pairs of DNA are found.Unlike heterochromatin, in euchromatin, there is little condensation to reach the genetic material.

In laboratory tests, euchromatin can be identified under an optical microscope because, being more isolated, its structure is impregnated with a lighter colour.

In prokaryotic cells, it is the only form of chromatin, this may be due to the fact that the heterochromatin structure has evolved over the years.

Euchromatin vs Heterochromatin

Euchromatin and heterochromatin are two structural forms of DNA in the genome, found in the nucleus. Euchromatin is the loosely packed form of DNA, found in the inner body of the nucleus. Heterochromatin is a tightly packed form of DNA, found at the periphery of the nucleus. Euchromatin makes up about 90% of the human genome. The main difference between euchromatin and heterochromatin is that euchromatin consists of transcriptionally active regions of DNA whereas heterochromatin consists of transcriptionally inactive DNA regions in the genome .

what is euchromatin

The loosely packed form of chromatin is called euchromatin. After cell division, DNA becomes loosely packed and exists as chromatin. Chromatin is formed by the condensation of DNA with histone proteins, which display beads on a string like structure. Euchromatin contains transcriptionally active sites of the genome. Parts of the genome, which contain active genes in the genome, are loosely packed to allow transcription of these genes to occur. The frequency of chromosomal crossings is high in euchromatin, making the euchromatic DNA genetically active. Euchromatin regions in the genome can be viewed under the microscope as loops, consisting of 40 to 100 kb regions of DNA. The diameter of the chromatin fiber in euchromatin is 30 nm. Matrix Connected Areas (MARs), Those containing AT-rich DNA are attached to euchromatin ends in the nuclear matrix. Euchromatin is shown in number 5

1 – nuclear envelope, 2 – ribosome, 3 – nuclear pore, 4 – nucleolus, 5 – euchromatin, 6 – outer membrane, 7 – RER, 8 – heterochromatin

function of euchromatin

Euchromatin is both transcriptome and genetically active. mRNA is synthesized to activate genes encoding functional proteins in euchromatin regions. The regulation of genes is also allowed by the interaction of regulatory elements in euchromatic regions. The transformation of euchromatin into heterochromatin and vice versa can be considered as a gene regulation mechanism. Housekeeping genes, which are always active, are present in the form of euchromatin. (Euchromatin vs Heterochromatin)

what is heterochromatin

The tightly packed form of DNA in the nucleus is called heterochromatin. However, heterochromatin is less compact than metaphase DNA. Staining of non-dividing cells in the nucleus under the light microscope displays two distinct areas depending on the intensity of the staining. Lightly stained areas are considered to be euchromatin, whereas darkly stained areas are considered to be heterochromatin. The heterochromatin organization is more compact in such a way that their DNA is inaccessible to proteins that are involved in gene expression. Genetic events such as chromosomal crossing over are avoided by the compact nature of heterochromatin. Therefore, heterochromatin is considered to be transcriptionally and genetically inactive. Two heterochromatin types can be identified in the nucleus: constitutive heterochromatin and facultative heterochromatin.

Constitutional Heterochromatin

Constitutive heterochromatin has no genes in it, so it can be retained in its compact structure even during cell interphase. It is a permanent feature of the nucleus of the cell. The DNA in the telomeric and centromeric regions belong to constitutive heterochromatin. Certain regions in chromosomes are related to constitutive heterochromatin; For example, most regions of the Y chromosome are constitutively heterochromatic.

resultant heterochromatin

The resulting heterochromatin incorporates inactive genes into the genome; Therefore, it is not a permanent feature of the nucleus of the cell, but can be seen in the nucleus for some time. These dormant genes may be inactive in some cells or over a period of time. When those genes are inactive, they form facultative heterochromatin. Chromatin structures, beads on a string, 30 nm fiber, active chromosomes in interphase are shown.

function of heterochromatin

Heterochromatin is mainly involved in maintaining the integrity of the genome. The high packaging of heterochromatin allows gene expression to be regulated by keeping DNA regions inaccessible to proteins in gene expression. The formation of heterochromatin protects against damage at the ends of DNA due to its compact nature.

Difference Between Euchromatin and Heterochromatin


Euchromatin: Euchromatin is the uncoiled form of chromatin.

Heterochromatin : Heterochromatin is a part of chromosomes. It is tightly packed.

packaging intensity

Euchromatin: Euchromatin consists of chromatin fibers, and DNA is wrapped around the histone protein core. Hence, it is loosely packed.

Heterochromatin : Heterochromatin is a tightly packed form of DNA in chromosomes.

blur intensity

Euchromatin: Euchromatin is lightly stained. But, it is dark colored during mitosis.

Heterochromatin : Heterochromatin is darkly stained during interphase.

amount of DNA

Euchromatin: Euchromatin has a lower DNA density than heterochromatin.

Heterochromatin : Heterochromatin contains a high density of DNA.


Euchromatin: Euchromatin does not exhibit heteropycnosis.

Heterochromatin : Heterochromatin exhibits heteropycnosis.


Euchromatin: Euchromatin is found in both prokaryotes and eukaryotes.

Heterochromatin : Heterochromatin is found only in eukaryotes.

genetic activity

Euchromatin: Euchromatin is genetically active. This may be due to exposure to chromosomal cross over.

Heterochromatin : Heterochromatin is genetically inactive.

effect on phenotype

Euchromatin: The DNA in euchromatin is affected by genetic processes, changing alleles on it.

Heterochromatin: Since the DNA in heterochromatin is genetically inactive, the phenotype of an organism remains unchanged.

transcriptional activity

Euchromatin: Euchromatin consists of transcriptionally active regions.

Heterochromatin : Heterochromatin exhibits little or no transcriptional activity.

DNA replication

Euchromatin: Euchromatin is an early replication.

Heterochromatin : Heterochromatin is a late replication.


Euchromatin: A similar type of euchromatin is found in the nucleus.

Heterochromatin : Heterochromatin is composed of two types: constitutive heterochromatin and facultative heterochromatin.

location in the nucleus

Euchromatin: Euchromatin is present in the inner body of the nucleus.

Heterochromatin : Heterochromatin is present at the periphery of the nucleus.


Euchromatin: Euchromatin regions are not sticky.

Heterochromatin : Heterochromatin regions are sticky.


Euchromatin: Euchromatin allows genes to be transferred and genetic variations to occur.

Heterochromatin : Heterochromatin maintains the structural integrity of the genome and allows the regulation of gene expression.

Compaction / Decondensation

Euchromatin: Condensation and dissociation of DNA occurs during the period of the cell cycle.

Heterochromatin: Except for DNA replication, heterochromatin remains condensed during each period of the cell cycle.


Euchromatin and heterochromatin are two types of DNA structure found within the nucleus. Euchromatin consists of a loosely packed structure of chromatin fibers in the nucleus. Therefore, DNA in euchromatic regions are accessible for gene expression. Therefore, genes are actively transcribed in euchromatic regions. In contrast, DNA regions in heterochromatin are tightly packed and inaccessible to proteins, which are involved in gene expression. Therefore, formation of heterochromatin from gene-containing regions serves as a mechanism for gene regulation.

The nature of packaging in both euchromatin and heterochromatin can be identified with their staining pattern under the light microscope. Euchromatin with low DNA density is stained lightly and heterochromatin with high DNA density is darkly stained. The condensation and dissolution of euchromatin occurs during the cell cycle. But, heterochromatin remains condensed during the phases of the cell cycle except for DNA replication. Therefore, the main difference between euchromatin and heterochromatin lies in both their structure and function.

1. Cooper, Geoffrey M. “The Internal Organization of the Nucleus.” The Cell: A Molecular Approach. second edition. US National Library of Medicine, 01 Jan 1970. Web. 22 March 2017.
2.Brown, Terence A. “Access to the Genome”. Genome. second edition. US National Library of Medicine, 01 Jan 1970. Web. 22 March 2017.

Image Courtesy:
1. “Nucleus ER” by Magnus Menske (talk) – Nupedia