What would happen if sister chromatids separated first, in meiosis 1? What genetic differences would occur?

If the sister chromatids separated first, it would no longer be meiosis. It would be mitosis. In meiosis the purpose is to use reduction division to reach that goal of 4 haploid daughter cells. In mitosis you only get 2 diploid daughter cells. The step of separating the logous chromosomes is crucial for dividing the chromosome count in half.