The first phase of Mitosis is INTERPHASE. In which the "parent cell" begins to divide to reproduce. Also during interphase, chromosomes, which are inside the nucleus, are duplicated, or doubled. This doubling procedure insures that the next generation, or "daughter cells" will hold the correct kind and number of genes as the "parent cell". Chromosomes are made of large D.N.A. that carry the "hereditary instructions" of the cell.