Final answer:
During interphase, eukaryotic chromosomes exhibit distinct regions of heterochromatin and euchromatin, with the former containing inactive genes and the latter containing active genes, typically allowing easier access for enzymes involved in replication and transcription.
Step-by-step explanation:
In interphase, the phase of the cell cycle between mitoses, eukaryotic chromosomes are organised into distinct territories within the nucleus. These territories consist of heterochromatin and euchromatin. Heterochromatin, which stains darker due to its tightly packaged structure, typically contains genes that are not being expressed. This form of chromatin is often found at the centromere and telomeres of chromosomes. On the other hand, euchromatin is less densely packed, stains lightly and generally includes genes that are actively being transcribed. This less compacted structure allows replication and transcription enzymes easier access to the DNA.
Furthermore, during interphase, chromosomes are duplicated, resulting in sister chromatids held together at the centromere. The centromeric region is highly condensed and will appear as a constricted area under light microscopy.