Sister chromatids are two identical copies of a chromosome that are attached to one another. They form during replication when the DNA is copied. Each sister chromatid has the same genetic information as the other.Sister chromatids are two chromosomes that are attached and that have the same genetic information. They form during replication when the DNA is copied. This means that each sister chromatid has the same genes as the other. Sister chromatids stay together during cell division and move to opposite poles of the cell. This ensures that the daughter cells receive an identical set of chromosomes.