Answer
In mitosis, for instance, a cell divides to produce two replicas of itself. For each replica to be normal structurally and physically for the species it must have the same organelles (number and kinds) and even more importantly the same number and kinds of chromosomes and amount of DNA as the original cell had before mitosis. This means that before the original cell divides into two it mus double the number of chromosomes and the amount of DNA. This is effected by DNA replication which takes place during G1 and S phases of Interphase. Proper chromosome sharing obviates aneuploidy.
Work Step by Step
t DNA duplication before cytokinesis is necessary to ensure that each daughter cell gets the correct number of chromosomes (for the species) and the correct amount of DNA. In the case of meiosis DNA duplication and proper chromosome sharing and cytokinesis are necessary to avoid abnormal conditions like monosomy and trisomy.
