If chromosomes in mitosis behaved like the ones in meiosis I, then sister chromatids would not separate at anaphase of mitosis. This would then mean that either one daughter cell would get all of the chromosomes and be 4n while the other would get no nuclear DNA or that two copies of some chromosomes would go to one cell and two copies of others to the other daughter cell. In either case, the daughter cells would have an improper chromosomal constitution.
Work Step by Step
To figure out the answer, look for how the chromosomes behave in mitosis and in meiosis I. The text and the relevant figures in Chapters 10 and 11 show that the big difference is that sister chromatids separate in mitotic anaphase to becomes different chromosomes, one copy of each chromosome going to each daughter cell. In meiosis I, the sisters do not separate, which would lead to genetic abnormalities. Then, it is a question of where the joined sister chromatids would go--all to one cell or some here and some there.