Final answer:
Heterochromatin is the term for highly condensed chromatin during mitosis, as well as in the regions of centromeres and telomeres, which is less accessible for gene expression and critical for chromosome segregation during cell division.
Step-by-step explanation:
The highly condensed chromatin, such as during mitosis and in centromeres and telomeres, is known as heterochromatin. During mitosis, chromatin undergoes maximum condensation, forming distinguishable chromosomes. This condensation is vital for the proper segregation of the genetic material between daughter cells. Heterochromatin is typically less accessible to the machinery responsible for gene expression and is associated with regions of DNA where transcription is repressed.
Chromatin exists in two main forms: the tightly packaged heterochromatin and the less condensed euchromatin. Heterochromatin contains the genes that are not actively being transcribed and is found in specific regions such as centromeres and telomeres. During the cell cycle's interphase, the chromatin is less condensed but becomes highly compact during mitosis, ensuring chromosomes are appropriately organized and divided.