Which of the following is said to be transcriptionally active chromatin?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Euchromatin.
In the nucleus, DNA is wrapped around proteins to form chromatin. Some regions of chromatin are loosely packed and stain light. These are called euchromatin. Because the DNA here is open, RNA polymerase can reach the genes and copy them, so these regions are active in transcription. Other regions are densely packed and stain dark. These are called heterochromatin, and they are inactive.
Option (1) Heterochromatin. — Incorrect. Heterochromatin is densely packed, so its genes cannot be transcribed. It is inactive.
Option (2) Euchromatin. — Correct. Euchromatin is loosely packed, and it is said to be transcriptionally active.
Option (3) Both euchromatin and heterochromatin. — Incorrect. Only euchromatin is active. Heterochromatin is inactive.
NCERT Extract:
Packaging of DNA Helix – “… In a typical nucleus, some region of chromatin are loosely packed (and stains light) and are referred to as euchromatin. The chromatin that is more densely packed and stains dark are called as Heterochromatin. Euchromatin is said to be transcriptionally active chromatin, whereas heterochromatin is inactive.”