Euchromatin

In eukaryotes, chromatin exists in two primary forms based on its compaction level - euchromatin and heterochromatin.

During interphase, the euchromatin is dispersed in the nucleus and replicated throughout the S phase of the cell cycle.

Euchromatin is a gene-rich, less compact, and actively transcribed region of the chromatin. When fixed and viewed under a microscope, it appears as lightly stained regions because it can retain fewer stain particles.

In metaphase chromosomes, the lightly stained regions represent the euchromatin.

The histone tail amino acids of euchromatin are extensively acetylated. Acetylation increases the negative charge on histone proteins, locally reducing the histone-DNA affinity. This reduces the chromatin compaction, allowing easier access to DNA.