Question

Why does it exist two types of chromatin?

Why is heterochromatin so tightly packed and euchromatin is not?

Answer 1

The chromatin exists in compact and loose, heterochromatin and euchromatin..

Explanation:

1. The DNA strands wrap round the histone proteins like beads on the string. This site forms the euchromatin.
2. The histone proteins wrap round the DNA and form the compact structure the heterochromain.'Thank you

Answer 2

There are euchromatin and heterochromatin: mainly distinguished on the basis of --

• histological staining and
• appearance during interphase.

During interphase, most of the chromatin takes up light stain but a small amount of chromatin in eukaryotic nucleus appears very dark under microscope. The light areas are euchromatin while the dark patches are heterochromatin.

• It is thought that euchromatin is in more hydrated and loosely arranged condition. This also means DNA of these areas are engaged in active transcription.

• Heterochromatin is obviously in tightly packed condition and DNA of this area is also late replicating in nature. (Constitutive heterochromatin is made of repetitive sequences, i.e. the areas may lack genes which is not true for facultative heterochromatin.)

For some more, you may read this:
https://socratic.org/questions/what-is-constitutive-and-facultative-heterochromatin