What characterizes heterochromatin?

Heterochromatin is characterized by its highly compacted structure, which is typically associated with areas of the genome that are largely transcriptionally inactive. This compact configuration prevents most gene expression, as the DNA is not readily accessible to the transcription machinery that reads and translates genes into proteins. Heterochromatin plays an important role in maintaining the structural integrity of chromosomes, gene regulation, and the segregation of chromosomes during cell division.

While actively transcribed genes are commonly found in euchromatin, which is less densely packed and more accessible for transcription processes, heterochromatin's primary function involves maintaining a silenced state of the chromosomal regions it encompasses. Therefore, the compact nature of heterochromatin ensures that genes located within its structure are usually turned off or expressed at very low levels, distinguishing it clearly from regions where gene activity is prevalent. The presence of heterochromatin at the ends of chromosomes, known as telomeres, does not define its overall characteristics but speaks to its role in protecting chromosomal integrity rather than its functional inactivity in gene expression.