In general, sister chromatids are either of the two chromatids of the same chromosome joined together by a common centromere. Once sister chromatids have separated (during the anaphase of mitosis or the anaphase II of meiosis during sexual reproduction), the strands are called daughter chromosomes. non-sister chromatid, on the other hand, refers to either of the two chromatids of paired homologous chromosomes, that is, the pairing of a paternal chromosome and a maternal chromosome. Non-sister (homologous) chromatids form chiasmata to exchange genetic material during the prophase I of meiosis.