Milad T. answered 04/21/19
Experience High School/College Tutor Specializing in Chem. & Bio.
Heterochromatin is a condensed version of DNA while Euchromatin is the de-condensed version. Why does that matter? Well, when your DNA is in the heterochromatic /condensed state that means that a promoter of a given gene is likely blocked and your transcription factors (TF's) are unable to touch down on it. As a result, that gene is considered inactive. While in the Euchromatic/de-condensed state the promoter of a given gene is not blocked, so your TF's and DNA Pol. can tough down on the promoter. Therefore, the gene is said to be active.