What is the relationship between the concepts of chromatin and chromosomes? Are euchromatin and heterochromatin a part of chromosomes?

Answer 1

Chromosomes are the next level of organization above chromatin, so chromosomes are made of chromatin that has been packed together. It goes DNA, chromatin (wrapped around histones), then chromosomes from smallest to largest.

Heterochromatin is chromatin that is tightly wound and inaccessible to transcription/replication machinery (generally forming structural parts of chromosomes) while euchromatin is loosely packed and available to be transcribed/replicated.