Euchromatin vs heterochromatin - which statement is correct?

• A. Euchromatin is condensed and transcriptionally repressed; heterochromatin is less condensed and active.
• B. Euchromatin is less condensed and transcriptionally active; heterochromatin is highly condensed and repressed; remodeling alters accessibility.
• C. Both are equally transcriptionally active.
• D. Only euchromatin exists in bacteria.

Answer: (B)

The main idea here is that how tightly DNA is packaged into chromatin governs whether genes can be transcribed. Euchromatin is loosely packed, which makes DNA accessible to RNA polymerase and transcription factors, so genes in these regions are generally active. Heterochromatin is densely packed, restricting access to the transcription machinery and leading to gene repression. The cell can remodel chromatin—through nucleosome repositioning and histone modifications—to change accessibility and switch genes on or off as needed. In bacteria, this euchromatin/heterochromatin distinction doesn’t apply the same way because they lack true histone-based chromatin; DNA is organized differently and remains relatively more accessible, so the statement about only euchromatin existing in bacteria is incorrect.

So the best description is that euchromatin is less condensed and transcriptionally active, while heterochromatin is highly condensed and repressed, with remodeling altering accessibility.