Why is it important for chromosomes to be condensed during mitosis and decondensed during interphase?
During mitosis the major problem to be solved is the correct separation of chromosome sets among daughter cells. If chromosomes were decondensed long tiny fibers of DNA would be dispersed in cytoplasm after the karyotheca breaking and chromosomes could not be simply organized and pulled by the spindle fibers.
During interphase the function of chromosomes, i.e, of DNA molecules, is the synthesis of RNA and therefore of proteins. For this task it is necessary for functional molecular regions to be decondensed (these regions form the euchromatin). During interphase in addition DNA replication happens as a preparatory step for cell division. In this process it is fundamental for the exposition of DNA molecules to serve as templates to new DNA chains under production.