What is Heterochromatin?

Heterochromatin is a densely packed or condensed DNA which is distinguished by the intense staining when stained by nuclear stains. They also contain transcripts that are inactive.

It is present in a variety of variants, ranging from four or five states that are identified by a combination with epigenetic marks. It is possible that the staining caused by heterochromatin may lead to heteropycnosis. It is the different staining of regions of the chromosomes. This chromosome differs from euchromatin due to the fact that the genes that reside in these chromosomes are typically inactive and not expressed. Heterochromatin can be found in the nucleus, towards the peripheral region. It’s not even present in prokaryotic cells, which suggests that this type of cell appeared later in development.

The two most commonly used heterochromatins are facultative heterochromatin and constitutive heterochromatin. Constitutive heterochromatin generally contains DNA sequences that are identical throughout all cells belonging to similar species. It’s usually repetitive and occurs in structural forms such as centromeres and telomeres. The genes of constitutive heterochromatin may affect genes located in the chromosomes that are tightly packed.

In humans, the genes 1 9, 16, and the Y chromosomes of males have higher levels of heterochromatin. Facultative heterochromatin encapsulates genes that are normally shut down by various mechanisms. However unlike constitutive heterochromatin facultative chromatin encapsulates diverse genes in various organisms belonging to one species. The facultative chromosome does not appear to be repeated, but it has the identical structural components of constitutive heterochromatin.

The development of facultative heterochromatin can be controlled through the process known as morphogenesis, or differentiation. In humans there is a difference between the two X chromosomes found in females is activated as facultative heterochromatin whereas the other one is expressed in the euchromatin. Heterochromatin serves multiple purposes. One of them is the regulation of genes and chromosomes’ integrity. The tightly packed DNA contained in heterochromatin protects chromosomes from diverse protein components that could cause the adhesion of DNA, or the inadvertent destruction of chromosomes caused by endonucleases. In addition, heterochromatin allows gene regulation as well as the inheritance of epigenetic marker genes.

What is Euchromatin?

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 located in the nucleus’s center and comprises around 90 percent of the genome in an organism. Under an optical microscope it appears as bright-colored bands after staining. The entire euchromatin protein is uniformly stained. This does not cause heteropycnosis. When examined under an electron microscope it is, however, an elongated microfibril with a 10 nm diameter. Its structure could be described by a rolled set of beads within strings where the beads are called nucleosomes. The nucleosomes have histone proteins that cover the DNA in a specific amount around.

In euchromatin the wrap around histone proteins becomes loose, and consequently, DNA sequences may be easily accessible. Euchromatin’s conformation is believed to be controlled through a modified portion within the chromosome, referred to as the histone tail. Euchromatin is the only proof of chromosomes within the context that the genome is prokaryotic suggesting that this form developed prior to heterochromatin. Unlike heterochromatin, euchromatin doesn’t exist in two forms. It’s only a the constitutive euchromatin.

Euchromatin is crucial because it has genes that are translated into RNA, which is later transformed into proteins. The unfolded DNA structure within euchromatin permits regulatory proteins and RNA polymerases to bind the sequences, so that transcription can be initiated. The possibility exists for certain genes found in the euchromatin genome to transform into heterochromatin , if they aren’t transscribed and are no longer active.

The conversion of euchromatin heterochromatin functions as a mechanism to control the expression of genes and their replication. In this regard, some gene types, like the housekeeping genes, are always placed in an the conformation of euchromatin since they have to be replicated continuously and transscribed.

Difference between Heterochromatin and Euchromatin – Heterochromatin vs Euchromatin

Basis for Comparison	Heterochromatin	Euchromatin
Definition	Heterochromatin is a densely condensed DNA, which is distinguished by the intense staining when stained using nuclear stains as well as the transcriptionally active sequences.	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.
Staining	Heterochromatin is darkly stained with nuclear staining.	Euchromatin is lightly stained by nuclear staining.
DNA conformation	In heterochromatin, DNA is tightly condensed or bound. The DNA of heterochromatin is folded by the histone proteins.	In euchromatin the DNA is not tightly bound or compressed. The DNA contained in euchromatin has been unfolded into beads.
Genes	The heterochromatin genes are typically inactive.	The genes that are present in euchromatin may be active or will become active in the future during growth.
Transcription	Heterochromatin is transcriptionally-inactive.	Euchromatin is transcriptionally-active.
DNA-related content	Heterochromatin contains more DNA that is tightly compressed by the histone proteins.	Euchromatin is a little lower in DNA that is compressed lightly by the histone proteins.
Content in genome	Heterochromatin makes up a smaller portion in the human genome. It is found in humans and makes approximately 8-10% of the genome.	Euchromatin is a significant portion in the human genome. For humans, it accounts for around 90-92% part of our genome.
Found in	Heterochromatin can only be found in the eukaryotes.	Euchromatin can be found in both eukaryotes and prokaryotes.
Types	Heterochromatin is present in two forms, both facultative and constitutive heterochromatin.	Euchromatin is present in a single form: it is a constitutive Euchromatin is a single form.
The nucleus is the location of the HTML0.	Heterochromatin can be found on the periphery of nucleus.	Euchromatin is located within the inner lining of the nucleus.
Heteropycnosis	Heterochromatin is a heteropycnosis-producing protein.	Euchromatin doesn’t exhibit heteropycnosis.
Replicative	Heterochromatin is a late replication that reproduces later than euchromatin.	Euchromatin is one of the early replications which replicates prior to euchromatin.
Generic processes	Heterochromatin isn’t affected by genetic changes, provided that the alleles aren’t mutated.	Euchromatin can be affected due to a variety of genetic processes, which result in changes in the alleles.
Function	Heterochromatin is responsible for maintaining the genetic integrity and regulates gene expression.	Euchromatin allows genes to be transcribed , allowing variation can occur within genes.
Examples	Centromeres and Telomeres Barr bodies are a part of the X chromosomes gene 1, 9 and 16 in humans are examples of heterochromatin.	The chromosomes of the genome, with the exception of heterochromatin are examples of euchromatin.