Crossing over exchanges segments between which chromatids?

1. Sister chromatids are identical copies, so swapping between them would change nothing. 2. The useful exchange is between chromatids that belong to different homologs. 3. Those are the non sister chromatids of the homologous pair. 4. The swap mixes maternal and paternal segments onto one chromatid. 5. That recombination is the first of the mechanisms that make gametes genetically unique. _Source: OpenStax Biology 1e (CC BY 4.0), Chs 10 and 11, section 11.1 The Process of Meiosis_