Chromosomes are visible only during mitosis.  During interphase, the chromosomes are uncoiled and appear as indistinct thread like structures called chromatin.  Look at the diagram of mitosis in your text. Note that the chromatin material does not begin to condense until prophase.   During prophase, chromatin condensation is accomplished by an elaborate system of coiling.  It has been estimated that the X chromosome would be about 13 cm in length if fully stretched out.  What would be the difficulty of mitosis if condensation of chromatin material did not occur?  Why is it important for the chromosomes to be in the uncoiled state during interphase?