Constitutive heterochromatin domains are sections of DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 that occur throughout the chromosomes of eukaryotes, but particularly at the centromere

Centromere

A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment...

s and telomere

Telomere

A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...

s. They often consist of very highly condensed, repetitive DNA and are largely transcriptionally silent. These regions normally appear darkly stained in karyograms.

Unlike facultative heterochromatin, constitutive heterochromatin is never converted back into euchromatin. The regions of DNA that exist as constitutive heterochromatin will be the same for all cells of a given species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

.

Constituitive heterochromatin is stained specifically with the C-banding technique.