Final answer:
Heterochromatin is densely packed DNA and contains genes that are not expressed, while euchromatin is less dense and contains genes that are transcribed.
Step-by-step explanation:
In interphase, eukaryotic chromosomes have two distinct regions that can be distinguished by staining. The tightly packed region is known as heterochromatin, and the less dense region is known as euchromatin. Heterochromatin usually contains genes that are not expressed, and is found in the regions of the centromere and telomeres. The euchromatin usually contains genes that are transcribed, with DNA packaged around nucleosomes but not further compacted.